The persistence of the murders in North Carolina as an internal discussion among atheists or secularists seems a point on which I should chime in with some features that I've observed or thought of over that discourse.
Implicit bias research in psychology would be an essential response to be aware of. This suggests that people "other"-ize people from other social groups, such as people belonging to religious entities that are poorly understood or largely unknown, or people from other racial groups. Most commonly such research suggests biases when interacting with darker-skinned people, Africans for instance. And most of these forms of bias are more subtle than what we typically refer to as racist. These are not people who drop the n-bomb casually, or who tell or email each other racist jokes, and so on. But they may describe a 12 year old boy as a threatening monster who must be shot given a set of conditions that might result in a firm talking to for someone Caucasian. And they may see a Muslim family when engaged in a fairly mundane concern like a parking dispute and pour a little extra on the hot sauce, so to speak, that it may end up violently resolved rather than the usual inane and heated exchange. We do not know enough about the particulars of that situation to know whether this was an armed man who escalated a simple domestic dispute over parking into murder, or whether this was an armed man seeking to execute people who committed, or were perceived to, minor transgression for what amounts to prejudicial reasons that border on or track into a hate crime, as we might legally define it.
Most Americans are very familiar with "Christians", in so far as they can't walk outside without meeting someone who professes to be so affiliated, practices some of the traditional rituals, and holds some of the beliefs so required. There are some atheists who hold a degree of hostility toward such persons, and certainly many secularists can find the behavior and policy views of many Christians annoying, if not illegal. But by and large, most Christians are not "feared", in the sense of representing a direct threat to the life and safety of atheists in the US. Even religious extremists like Ken Ham or the WBC or Pat Robertson are mostly sources of mocking amusement for the absurd things they believe and say in public as even as there are substantial populations who agree with them, few of their most absurd beliefs are popular enough to mandate into legal actions (and none of those would withstand a court challenge). This is so even among anti-theists in many cases.
These are not commonly professed actions as it regards Muslims; who are seen as an actual or literal threat to Americans more broadly, and perhaps to secularity or a tangentially involved project like liberalism as well, in an existential or actively violent manner in these cases. And such activities and views are attributed to be unique threats posed by Muslims rather than Christians or Buddhists or other theistic views. Anti-theists in prominent public positions (Sam Harris for example) have expended a good degree of time and energy speaking or writing in professing this view, particularly post 9-11, often doing so while justifying a set of repressive policies or aggressive foreign policy interventions they prefer to see enacted (in Harris' case, profiling, torture, and invasions or assaults on several countries, and the possibility of pre-emptive nuclear strike should an "extremist" Islamic nation-state such as Iran obtain or be close to obtaining nuclear weapons, others have suggested severe immigration restrictions as a similar course of action). It would be reasonable given these views as accepted to apportion a certain degree of bias and animosity or fear toward the infrequent encounter an American citizen has with Muslims within the borders of the United States.
In as far as there are Muslims so identified as having committed atrocities, acts of aggression, violence, or terror around the world, these are indeed plausible fears. In so far as these are unique attributes, it tends to overlook the majority of violent incidents or events in both the US and the world or ascribes more comfortably to those events a non-religious basis for the activity. For instance, a border dispute could be framed in ethnic or national interests, rather than a religious conflict. The actions of a lone shooter or bomber can be viewed as the behavior of a deranged lunatic, or as part of a political ideology, rather than having religious connotation. Likewise, acts of terrorism are sometimes conveniently absolved or overlooked where they are or were committed widely by non-Muslims (the IRA, LRA, Tamil Tigers, various Mexican cartels, etc). All of this structure is intended to form and defend a narrative that these problems and tactics or strategies are unique to a particular religion. If such a narrative is true, it might be reasonable to respond to minor transgressions and forms of aggression by adherents to that faith with a degree of belligerence to dissuade future aggression, or to focus public attention and scrutiny and so on. If such narratives are not true, and are instead forms of cognitive bias, then such responses are unlikely to have much impact and will be viewed as needless and destructive meddling at best.
Unfortunately what is likely the case is that the situation is more complicated than these polar positions and this explains a great degree of the ability of both sides in such discussions to cherry pick examples of support. ISIS is not, for example, much of a significant threat to US security or US interests, or even to some of our regional allies or partners (Israel or Turkey for instance), and as such it seems unlikely that our involvement is likely to either succeed or be more effective than allowing regional powers to collaborate on a strategy to oppose them. But it is a regional threat professing and attempting to justify for itself a certain religious base for its ideological and territorial goals. In as far as it adopts a most extreme or warped interpretation of Islam's canonical texts and laws, it is little different from some Christian (or Hindu or Buddhist) groups who do likewise. But in as far as it actively controls or attempts to control and conquer territory through violent means, and represses alternative histories or ideologies/religions (by destroying artifacts or temples for instance), it is a uniquely dangerous world agent. None of this necessarily follows that our conclusions of action are and must be what are suggested by the more "belligerent" among the anti-theist community. Nor does it follow that this is either unique to Islam, or uniform belief and practice among Muslims.
The point would be that we should be cautious in recognizing that we may also have potential biases here, ill-informed by a lack of familiarity with people of a sometimes distinct cultural grounding.
In as far as this intersects with secularist or anti-theist communities specifically, one aspect that I feel tends to define secular communities is a desire to apportion belief and especially action based upon belief toward the best available evidence. That is: if we are to put forward a plan of action, that plan of action would be formed based upon our best understanding of what should or has worked and which ideas have failed to work or seem unlikely to succeed given the available alternatives. If we are to support a policy of torture, or invasion and nation-building, or use security and police to profile particular persons, or to identify a unique danger of particular kinds of countries having nuclear arsenals, it behooves us to examine the likelihood of those projects having the intended effects and succeeding, or whether we are in fact overinflating the dangers in order to justify particular belligerence.
Profiling for instance has a long history of use in policing. It has limited utility in deterring ordinary crime versus digging up a lot of suspicious stops and searches by police instead. Given the NYPD and FBI's use in counter-terrorism, it seems to have zero practical use in deterring and detecting terrorist activity also. The NYPD followed Muslims around for years and generated zero leads or arrests, for example. While several of the terrorist attacks that occurred were warned about, often by other Muslims, and often little action was taken. Similarly, we can point to torture's lack of identifiable results, and severe departure from the special case exemptions that many people might find morally plausible (the "ticking time bomb"), to suggest that neither of these are policies that will have a beneficial effect upon American's marginal security, and may actually be damaging in so far as they may enrage the populations that are so afflicted by them, or at least demonstrate a double standard or hypocrisy in the profession and insistence of the protection of human rights, as they apply to all people. Likewise, we can point to the rogue state of North Korea and its nuclear arsenal, or to the rather immoderate and "backward" Muslim-majority state of Pakistan to suggest that the "Iranian-death-cult" theory favored by many belligerents in the Iranian, or previously the Iraqi, discussions are misplaced or overblown fears. The world has lived with the threat of nuclear annihilation for 60 years and for the last dozen or so has stomached the emergence of more unstable powers to the nuclear club without the world ending. And I think the examples of Iraq, Afghanistan, Kosovo, Sudan, Libya, and others over the last two decades suggest that nation-building and regime changes are unlikely to succeed in solving our problems with these other countries, to say nothing of the destruction our campaigns can inflict upon the people living there and whether such things as a military campaign on our part will result in a better circumstance for the country and its people itself that we should claim it was on their behalf. Against this, it seems questionable why people who profess to be guided by evidence and reason would persist in demanding similar attempts at these same policies for years at a time. It might even be reasonable to assume a degree of bias is involved if they are unwilling or unable to consider other options as more effective or necessary, or even unwilling to consider the ineffectiveness of their own preferences even if they assume other methods would be non-meaningful and effective instead.
A further complication is one often seen in analysis of religious communities themselves. This would be that the adherents of religiously conceived beliefs and practices and rituals are not always in step with a leadership or theological scholarship of those beliefs, practices and rituals. It may be that leaders profess or stress very different passages, interpretations vary widely, and in general may practice a faith in a very different way than those who consider themselves to be listening attentively to such guidance. One reason for this may be that we are selective in what we want to hear or accept as beliefs ourselves, and another more nefarious construction would be that we are often selective about what we tell other people we ourselves believe, sometimes for manipulative purposes and ends. As a more religious example, Bill O'Reilly was commonly portrayed by some as insisting on the death of George Tiller by publicly identifying him as a murderer of babies through his work in an abortion clinic. O'Reilly never calls for his death specifically, but in identifying another person as a commissioner of actions commonly perceived as heinous, more radical adherents to those beliefs perhaps took this to be a signal of identifying a particularly egregious individual worthy of assault or death by those actions. Political speech also strays into this realm (the Palin map with bullseyes upon various Congressional districts, followed by a personal attack on one of these Congress members in Arizona). It is not clear that all such cases like this intend on the death of those identified, or that the commission of the acts themselves were at all tied to the public declarations in the first place (many are not). What can be clear is that if a group does not wish to be publicly associated with such actions, they may choose their claims and battles carefully, perhaps avoiding the most incendiary claims or demands for action. Antitheists are not typically advancing "militant" or "radical" claims, departing substantially from atheists or secularists more broadly. But they are more likely to evince a degree of hostility toward the concept or practice of faith by other human beings. Atheists are no more likely to be entirely a population of calm, rational people, even as they are less likely to be commissioners of ordinary violence and crime, which to me suggests that inflammatory rhetoric carries no less risks to be used by atheists and antitheists than it does when anyone else does it, that it may err to stray forward to invite violence even if as a philosophy, humanists and secularists will work to condemn such actions.
Bear in mind that various religious orders frequently disavow any approval for acts of violence or terrorism purportedly committed in their name, and these disavowals may fall upon deaf ears and go ignored by those insisting that such groups should disavow such violent methods, particularly where such groups are in the minority as Muslims (and atheists) are, and we should recognize the dangers involved in putting forward even the modicum of force and violence in our ideas versus the forceful presentation of ideas and arguments.
Anti-theism does well in stressing critiques of religious orthodoxies and dogmas in the destructive potential such beliefs and practices can inflict. It should be careful not to assume that these define the whole of religious practice and belief, when they plainly do not, or to assume that such critiques should be backed with violent intention, as some have insisted at the policy level (not at the individual level). It should be a reasoned response to the dangers of a fervently theocratic society, and cognizant of the actual ability of "outsiders" to affect swift and just changes upon societies and states disordered relative to a progressive liberal status quo sought by Western powers. The caution I would demand for the first point is twofold. Avoid broad-brush guilt by association behavior. This will generally place many people who have little common cause with terrorists, extremists, or religious fundamentalists on the defensive rather than leaving such people open to ameliorating the worst injustices of their beliefs as practiced and as afflicted upon societies at large. Secondly it focuses public attention upon those more egregious and dangerous and prejudicial behaviors rather than much smaller transgressions and works to place such behavior and practice of faith in that way to be out of bounds in a polite, tolerant society. The avoidance of violent means unless absolutely necessary, such as in self-defence, also should be stressed anywhere a response is needed to those forms of aggression by religious agents. The application of force and violence should be reserved, and the resolution of disputes sought out through the arenas of free speech and debate through the political process where ever possible.
I do not think that most secularists or anti-theists are spending time and energy and effort demanding violent revolution against religion, or insisting upon violent means of resolving our disputes with such. Much of what is painted as "radical/militant atheist views" is pretty standard: that religious orders or beliefs can be harmful, for example. And this is not very controversial, even among many religious persons that their faiths have flaws in practice or outdated concepts of belief that they no longer practice.
I do think that much of the advocacy for militant action either via force or politically via specific police powers against particular groups is counter-productive for Western educated and residing secularists. Not because Islamic militant groups like ISIS are not dangerous and do not deserve any public attention as a cause worth attending to by someone (intelligence agencies for example, or other Islamic countries or groups that are more locally threatened). But because they and their views are not representative of the much larger but diverse and spread out populations of Muslims most Westerners would ever encounter at home, and are thus unlikely to directly or existentially threaten Americans or Europeans in a meaningful way. Nor are the actions and atrocities of such agents in places that we would have considerable influence and the power to prevent them and by which we should want to spend that much time and attention worrying about the behavior and violence until such a point that we might possess the power and understanding to sway and influence to prevent such actions. Meanwhile various Christian groups are much more numerous and active and organized politically to influence public policy in what seems to a humanist ethic a negative way, and are often using western influence and interventionism to influence local policies (as an example: Uganda and the attempts at very stern, potentially lethal, anti-homosexuality bills were heavily influenced by American missionaries and anti-homosexuality propaganda). We have the power and influence to prevent these things. It is still anti-theist in nature to work against the propagation of religious ideas through public policy, and, more to the point, we are seeing progress on these fronts as states and nations adopt tolerance of consensual homosexual partnerships or traditional "vice" crimes like the consumption of certain narcotic substances.
I do not think this means that secularists and anti-theists should spend no time and attention speaking out against atrocities or human rights violations pertaining to the Islamic world, nor that they should not advocate for violent methods of reprisal should such violations be made upon ourselves as well, or that people cannot advocate for their views more broadly as they apply to the purported dangers of various religious entities. These are indeed problems afflicting millions of human beings on the globe and we should be sympathetic to the issue and attentive to opportunities to resolve or alleviate such suffering where we can. But I do think that the unique approaches called for in combating the purported Islamic threats are either ineffective, based on the evidence, or simply not likely to produce a positive effect, and that the amount of time and effort expended by some suggests an unhealthy level of worry and concern over these abuses and issues for which we have limits on our time and ability to control such. More over, I do think that it is possible the anti-theist view can become too narrowly associated with these views, of anti-Islamic views in particular and by this often strays into Islamophobic attitudes which can stereotype or position any or all Muslims as a potential threat to liberal ideals or the western lifestyle, or whatever. This should be avoided as such stereotypes are unhelpful both to the cause of advancing a secular mindset/worldview and to opposing and highlighting the actual dangers and harms performed by religious orders upon actual human beings.