But a vote for a losing candidate is not "thrown away"; it sends a message to mainstream candidates that you vote, but they have to work harder to appeal to your interest group to get your vote.
Such actions send a lot of messages. I have no confidence in the ability of politicians to determine what I would be trying to convey or the effectiveness of my attempting to do so.
Besides, the point is trivial. A vote for a losing candidate isn't thrown away because the vote almost certainly couldn't have been used productively in the first place - you lose little by casting it for the candidate you prefer, just as you'd lose little by casting it for any of the ones you didn't.
Not voting also sends messages to politicians and your fellow citizens. It is not obvious that they are worse than the ones you'd send by voting.
At a Foresight Gathering some years ago, a Congressman was in attendance, and he spoke to us and said the following:
Many hands went up.
Fewer hands went up.
Rationalists would likewise do well to keep this lesson in mind.
(I should also mention that voting is a Newcomblike problem. As I don't believe rational agents should defect in the 100fold iterated prisoner's dilemma, I don't buy the idea that rational agents don't vote .)
(See also Stop Voting For Nincompoops. It's more applicable to primaries than to the general election. But a vote for a losing candidate is not "thrown away"; it sends a message to mainstream candidates that you vote, but they have to work harder to appeal to your interest group to get your vote. Readers in non-swing states especially should consider what message they're sending with their vote before voting for any candidate, in any election, that they don't actually like.)