and old thread continues.

I'd have to say that tolerating the lifestyles of people who can do things like that, who enjoy sexual contact without associating it with romantic entanglements but still have fulfilling relationships in spite of this supposed moral character flaw is kind of something society has little business in worrying about (provided they can do so "responsibly").

That it doesn't seem like it's something that will be promoted because it's (certainly) not a majority of the population is entirely different from whether or not
a) it happens
b) people enjoy permissible extramarital/extra-relational sexual contact perfectly fine with or without our moral approval of it.

Where I have a problem is still the hypocrisy of people who denigrate people who do live like this and then who go out and have secret (ie, non-permissible) affairs, presumably because such affairs would not be approved of if they were sought after or more importantly they would not be approved of because they would be seen as harmful and hurtful actions whether they were permitted or not or known about or not. That to me seems far more fucked up than actively coordinating a more complicated and active sexual lifestyle within the context of a couple. And yet it's a lot more common for people to cheat than the number people who can do so freely and permissibly in open relationships.

This is one of these very strange moral problems where I see no problem but a vast majority of the general public seems to think this is a big deal and almost an absolute moral no-no. If the people involved do not see a problem and do not have a problem with their partner's behavior and can still lead happy or productive lives, I'm hard pressed to see what business we have telling them that they should do things "our way".

People are right to see the homosexuality morality debate as related to one on polyamory to the extent that both are actually about what consenting adults do with one another and our misbegotten legal "abilities" to punish consensual actions. I do think that contractual arrangements for a polyamorous relationship would be more complicated to enforce or implement, but then I think normal marriage contracts should be generally more complicated too than they are (that they should admit of the possibility of failure for example in the same way that people should carry out living will consultations for medical conditions). I don't think it should be that hard for us to admit however that there are some people who can form strong intimate bonds with someone for relationship purposes and not associate their sex life with that bond, such that they can then go have other sexual relations. Presumably the problem with it is that this is something like
a) It's not typically a "both" scenario. One person doesn't go have "free love" but rather wants the other more.
b) Other people would worry that one or the other person might become more attached to some other person by having sex with them, or having sex with some other person more exclusively than with their spouse/significant other. That indeed is an interesting problem. But it's more "our" problem reflected into the scenario (we would not like this arrangement very much of a spouse having extra sexual attentions) than it is necessarily "their" problem.

Additionally, I don't see how this relates to the problem of marriage rights being tied (ridiculously) to child-bearing/child-rearing. For one thing, it would be enough under that logic for any two people to be "married" even if they are straight but do not have sex with each other, or if they are both of the same sex but not romantically or sexually involved at all (ie, not homosexual), and who adopt a child or have a child from some other arrangement. We don't have very firm legal standing for this as an arrangement for adoption, but we also don't have a very firm legal (much less moral) standing that people who have children must be married, or that people who get married must announce an intention or demonstrate an ability to procreate. None of these things directly associates with sexual infidelity.

We do have marriages and relationships that fall apart from infidelity, and some of them produced children and this is indeed a big problem. But to me these are two separate issues. One is parental rights and the promotion of an "ideal" family environment for children to be raised in. And the other is the sexual health of our intimate relationships. The first can be addressed much more forcefully by removing our fixation on infidelity and homosexuals or a fixation that the two people who have and produce a child should be the ones who raise it and simply focusing on the needs that children have to produce good outcomes for them (this also raises questions about things like surrogacy, adoption, or even the methods by which people might be considered good foster care). And the second should be addressed by encouraging a more active sexual correspondence within a couple. Couples should be aware that their partner may have strong extramarital/extra-relational sexual wants and needs and if this is unacceptable or uncomfortable, they can end the relationship. Or they can be aware of it and tolerate or even participate and promote such things. This should be up to the couple itself to design and to determine their reactions and feelings and any ground rules involved. But it would be far healthier if our society did not encourage a hypocrisy by socially and culturally commanding that people who have these sexual wants and needs must live in secret with them from their intimate partners (and thus potentially risk harm to those same partners).

Certainly I think it wise that most of us consider the wants and needs of our partners, and I think if there is an open dialogue most of us may express a desire, but not ultimately act upon that desire. After all it is easy enough to find many people attractive. It is less easy to engage many people in sexual relationships for the hurt that it may cause when we might do so. But we cannot even acknowledge this potential for a hurt to exist unless we consider having the debate with each other and being expressive of it rather than hiding it away.