Andrew Gelman defends the most basic one:
If your vote is decisive, it will make a difference for 300 million people. If you think your preferred candidate could bring the equivalent of a $50 improvement in the quality of life to the average American--not an implausible hope, given the size of the Federal budget and the impact of decisions in foreign policy, health, the courts, and other areas--you're now buying a $1.5 billion lottery ticket. With this payoff, a 1 in 10 million chance of being decisive isn't bad odds.
2006-2011 archives for The Daily Dish, featuring Andrew Sullivan