Suppose I decide to vote for Bob Barr, the Libertarian candidate, who will assuredly lose the presidential election this year. Further suppose that my least favorite of the two major candidates wins the election by carrying my state by one vote. I guess I would regret my vote for Barr.
What are the odds that I would regret my vote for Barr? In the tightest election in decades, a few hundred votes in Florida separated Al Gore and George Bush. If any single voter had switched his/her vote . . . there would have been no difference in the outcome.
My vote this will almost certainly not matter.
But, you say, what if everyone felt that way? If no one voted, I would want to vote, so that I could decide the election. But that event in a presidential election is equivalent to a thermodynamic impossibility--about as likely that I will spontaneously combust.
So my vote is entertainment. I enjoy voting. Voting gives me a sense of community--of being a part of something old and large and good. Republicans and Democrats do not form the same kind of community for me. I do not get a thrill from voting for either.
But I do enjoy voting in favor of freedom. So if a candidate stood for the rights to life, liberty, and the pursuit of happiness (property rights), I enjoy voting for her.
(No candidate would be crazy enough to do that. The press would take an axe to someone who was actually in favor of the right to free speech/religion/association/etc.)
So if I enjoy casting my vote, then it has done its duty. It doesn't have to make a difference.