In a situation where you strongly disagree with both candidates, knowing who is projected to win in advance should motivate you to vote for the loser. That way you have a clear conscience because none of the bad things that McCain would have done will happen anyway while all of the bad things that Obama will do actually do get to happen. The problem is that people don’t think about these things rationally. The objective of voting should be to be able to live with yourself afterwards and not to jump on the bandwagon of the winning team.
That’s the exact opposite of how most people think. They want to be on the winning side; to “back the strong horse”, as a certain cave-bound Obama supporter might say.