By voting, you will not make (or probably even encourage) every jaded rationalist in America to vote, so from a decision theoretical standpoint that observation is irrelevant.

That's not quite what I meant. If people think similarly to you, then they will most likely make similar decisions as you. Now that I've suggested this to you, you think similarly to all the people out there who realised this themselves or had someone point it out to them. So when you decide whether or not to vote, you should do so in the knowledge that there are a bunch of people out there who will probably end up making the same decision as you purely because they think similarly to you. You're not just deciding for yourself, you're deciding for everyone who thinks like you.

EDIT: Also, I disagree with you about the negative effects of compulsory voting. There are definitely some, but I think the negative effects of NON-compulsory voting are potentially worse. See my comment to Drethelin below.