Voting once again seems to be under general discussion for some reason.
Alex Tabarrok at MR links to an article by Gelman and Kaplan, which points out that while the benefits of voting are small (because of the very tiny probability of one vote changing the result), they affect millions of people. If I am a little bit altruistic - say, if it is worth 10 dollars to me to make some other person 100 dollars better off - then the actual benefit of changing the result can easily be bumped up into the billions, which could make it worth heading off to the voting booth even with a one-in-ten-million or so chance of changing the outcome.
The fact that so many people make charitable donations - where doing 100 dollars of benefit costs 100 dollars plus some overhead - implies that the 10% coefficient I use above is very plausible.
(To be clear, we're not just talking about cash benefits here. I might consider it a benefit worth $100 to me to have someone else sent to university, or treated for a disease)
The Gelman and Kaplan argument is so obviously correct - not just logically sound but the real reason why people do actually vote - that I'm embarrassed to have spent so much time looking for alternatives.
Is everything rosy with democracy then? Unfortunately, I think G & K stopped a bit too soon. After all, altruism is real, but it's not the only motive out there on top of selfishness.
Let's say I have a particular hatred of muslims. It might be worth $10000 to me to cause the death of a muslim. By changing government, I might kill thousands of them! That would be worth a lot more to me than a cut in sugar tariffs.
But is $10,000 realistic? It's surely not that hard to get someone killed if you have a few grand to spend on it - we'd be up to our knees in corpses. But in normal life, the main cost of killing someone is the risk of being caught and punished. And plenty of people get killed anyway. Democracy isn't just a way of having an effect (good or bad) on millions of people; it's a way of doing so with total impunity.
The arithmetic I'm throwing around here isn't really rigorous. What does it mean to say that I value a better house for a poor family at $200, or someone else prevented from playing online poker at $100, when I have no way of directly causing these things to happen? It doesn't matter. The original question is: is it worth 30 minutes of my time to have a 1-in-10-million chance of causing a million poor families to get better housing, and to stop five million people from playing poker, and to cause 100,000 muslims to become dead muslims? (etc.) If those are the things I want, it might well be.
Is this good or bad? I think most people are more altruistic than anti-altruistic, at least towards their own countrymen. So voters should be expected to vote mostly for the general benefit as they see it, but perhaps be a bit on the warlike side. The impunity thing, though, has some nasty implications. The large-scale altruism expressed through voting is in some degree in competition with direct small-scale altruism, but the "effectiveness multiplier" of democracy is greater in the case of punishing others, because it detaches the harm from any responsibility.
Anti-altruism isn't always a bad thing. A certain level of vindictiveness benefits society by discouraging anti-social behaviour, even in those circumstances where Homo Economicus would rather cut his losses. But I worry that when detached from the human scale, the natural willingness to punish individual enemies becomes a generalized animus against everyone resembling some enemy.
Finally, none of this contradicts Bryan Caplan's critique of voters. The individual benefits come from the good feelings of believing I have had the influence I desired. I can still have those good feelings without putting in the effort to convince myself that the effects will be what I expect. "I personally stopped a million people from eating trans fats in restaurants". If that gives me the good feelings, it would be silly to put lots of effort into working out whether it actually did anyone any material good. The costs of being wrong are tiny.