Belief is more a social process than a rational one.

Miguel at Simoleon Sense has been looking at the extensive Less Wrong Blog "a community blog devoted to refining the art of human rationality." Here is Miguel's summary of a key theme there.

How To Actually Change Your Mind: A collection of blog posts - via Less Wrong -People go funny in the head when talking about politics. The evolutionary reasons for this are so obvious as to be worth belaboring: In the ancestral environment, politics was a matter of life and death. And sex, and wealth, and allies, and reputation… When, today, you get into an argument about whether "we" ought to raise the minimum wage, you're executing adaptations for an ancestral environment where being on the wrong side of the argument could get you killed… Politics is an extension of war by other means. Arguments are soldiers. Once you know which side you're on, you must support all arguments of that side, and attack all arguments that appear to favor the enemy side; otherwise it's like stabbing your soldiers in the back – providing aid and comfort to the enemy.

Just to be clear, I'm pretty sure Miguel's summary is meant to describe a widespread phenomenon, not to recommend it.