Some of the stupidest and worst-informed people I've ever met have been liberals, and some of the most intelligent and thoughtful people I've met (and I've met quite a number) have been conservatives. I spent four years at Georgetown, which is probably one of the most politically active schools in the country, so I think I have a decent sample of both the left and the right (albeit biased towards the intelligent end - but not as much as you might think, trust me).

This isn't a particularly robust article, but the point he makes is probably correct - intelligence makes one more likely to go to university, and going to university exposes one up to far more liberal influence than conservative. It certainly matches my experience. My experience has also been that the vast majority of liberals move at least a bit to the right after they grow up and have to support themselves.

(No one's ever totally objective about this stuff, but for what it's worth, I'm a moderate, to the point that I didn't feel I could vote either way in the last election.)