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.