But neither does voting for a candidate that you know ahead of time won't get more than a small percentage of the vote.
If enough people of a progressive persuasion took active participation in the Democratic Party, made their stance known, and kicked some butt if necessary, instead of sitting back and sulking, it would fix the problem.
In 2004, I argued like hell for Dennis Kucinich in my precinct caucus and was sufficiently persuasive to swing a lot of votes his way--even to the extent of being asked to be a delegate to the state convention. Due to circumstances beyond my control, I was unable to accept. BUT--I saw what one voice, my own, speaking with passion and conviction, could do.
Kucinich didn't get the nomination. But he had more delegates coming out of Washington State than he would have had, had I not done what it did. I was only one person, but I managed that. So I have a pretty good, in-the-trenches idea of what can be done if enough people get involved. That's the way democracy is supposed to work.
I absolutely refuse to simply throw up my hands and say, "Why bother? It's hopeless!?