I say this about every year. It gets old.
Telling people they can't complain if they don't vote doesn't make any sense. Don't do it. You look like an arrogant prick who isn't paying attention. Basically you come off like one of those door-to-door missionaries who isn't aware that most everyone in the area is a Christian already but with a sales pitch that sounds like there's a lot of people like me out there. People who are voting, people we "want" voting, are already doing so in pretty hefty amounts and the types of people complaining about politics are especially.
Chances are excellent that the only people paying attention enough to complain in a cogent way did vote. And the reason they're now complaining is that stupid things are going on anyway in spite of their participation in elections. Their awareness of stupid things implies they are paying attention and likely voters. You don't need to sell them on the prospect by talking it up. Voting offers a very small chance of changing the stupidity to a different format with very minimal effort on the individual's part. All you technically have to do is register and show up and cast a ballot, no attention is required to matters political to vote. People who pay no attention to it probably aren't the kinds of people we want showing up, because they're more prone to systemic biases that are harmful, like racism/sexism/anti-immigrant bias and misinformation on basic facts. But chances are, someone who complains about politics, that person did vote. Even if they were ill-informed or under-informed about the basic issues.
Second, even if they don't vote, the chances their votes are the best method of changing that stupid thing from going on is still extremely small. In fact it is likely that someone complaining about it on Facebook (and doing nothing else, itself a troubling prospect) has an equal or greater chance of influencing public policy than their vote by influencing public discourse in some small way. There are dozens of ways to execute your civic duties to fellow citizens, and voting is a very, very small one. It's probably one of the least effective in fact because it has only a limited impact upon what policies are enacted and what laws will govern us compared to the alternatives. The assumption of "not voting" canceling out these other active alternatives in a person's routine engagement with matters civic and political is extremely arrogant and dismissive. People can care a great deal about their fellow citizens and express it in often very meaningful ways without bothering in partisan political discourse decided in a ballot box.
Telling people they can't complain if they don't vote is basically a stealth way of exhorting people to go vote through some variety of shame, as if in a bizarre secular ritual. As implied above, voting is a minimal standard of civic engagement. What you should be exhorting people to do is pay attention and maybe get involved in some issue or other that they/you believe requires reform. And then do so yourself. Telling people just to go vote, with no other recourse to civic involvement, is like saying "I know you can't be bothered to give a shit about other people, so at least pretend like you did in this very small but publicly celebrated way." We are rewarding ourselves for paying attention at a point which has very little impact and allowing ourselves permission through that social congratulation to ignore it the rest of the time. It's the rest of the time that stuff is going down people. That's when you pay attention and get involved if you wanted something to happen (or not to). Not one day in November. Some random day in March or July is when a bill gets into public discussion or a judge decides an important case.
If you want to vote, great. Fine. I'm not complaining that people do this in the slightest. You're welcome to do it. I think it should be easy to do and that people aren't prevented or restricted from doing so. For instance, I think states that prevent ex-cons from voting should not do so, and that voter ID laws are extremely dumb ways of addressing any probable causes of voter fraud and basically clumsy racism dressed up as something else. I don't advocate things like civic knowledge tests or basic political or demographic knowledge tests either (there's no chance those could be administered fairly for one). What I'm concerned about is how people go about talking about voting as though it's the greatest thing ever and that people who don't do it are losers or something. Sliced bread sucks too. I'm tired of hearing about how great it is (supposedly). But at least most people don't go around saying that unsliced bread is something awful and pitiful. They instead talk about the virtues of sliced bread in comparison to other supposedly great things. Politics is a lot bigger than our yearly elections and there are many, many more productive ways to plug yourself into it than entering a ballot box once in a while. Don't try to tell us this way is the most awesomest one ever. Just go do it.
And then complain about all the people who you voted against winning like the rest of us do.
There are two corollaries to this line of argument I think are worth suggesting as well.
1) Other countries with highly corrupt and illiberal governance have elections, they can even have "free and fair" elections in order to elect what amount to dictators or theocratic parties (Iraq, Iran, Palestine/Gaza, Egypt, Russia, etc). This is evidence that "voting" is a pretty minimal standard of civic involvement for a modern liberal democracy to practice. Voting is probably one of the least important institutions to maintain and participate in order to exercise one's liberty as a citizen in a (relatively) free state. Majoritarian rule through election contests is a pretty minimal standard for western liberalism to be practiced and isn't the central feature of those nation-states that ascribe and aspire to it. It's a feature, but it's primarily about the protection of minority (and individual) rights that one could say a defining character of a liberal democratic state is found.
2) Voting often results in people we don't like winning elections and instituting or attempting to institute bad policies. It could be as simple as our "red vs blue" fixation, but in other countries the results could be something like "Hamas". One of the problems with American coverage of the Iranian election protests was the assumption being that the liberal student protests were evidence of a broader support for revolution of the Iranian system of theocratic and illiberal democratic elections. They weren't. But we were willing to go along with that assumption because the people we didn't like had won the elections and it was assumed the people who lost supported our agenda (as a hint: they didn't).
This isn't evidence that voting is inherently awful, a complaint I've seen some libertarians make (which is a problem among libertarians). But if the general public tends to actually support things that are reprehensibly bad, and for whatever reason they often do on a lot of public policy questions, the way to change that isn't going to be through counting the ballots up every year, because those ballots will just continue to document the awful preferences of the majority. It's going to require a lot of hard work and engagement with many, many people. Legalization of marijuana or the acceptance of gay marriage equality have taken decades of agitation, and the battle was waged in newspapers and press editorials, street canvasing and petitioning, marches or demonstrations, even expressions in popular culture. And of course fought in courtrooms to overturn bad laws. Ballots are only a fairly recent addition to these campaigns. This suggests that voting is a low priority civic subject compared to all the groundwork that goes into getting something as even an option to vote on, where the candidates consider the issue worth legislating or popular referendums are introduced, and so on.
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