Michael Shermer: Intelligence Good At Rationalizing Beliefs.

Once people commit to a belief, the smarter they are, the better they are at rationalizing those beliefs. Thus, smart people believe weird things because they're skilled at defending beliefs they arrived at for non-smart reasons. Most people most of the time arrive at their beliefs for a host of reasons involving personality and temperament, family dynamics and cultural background, parents and siblings, peer groups and teachers, education and books, mentors and heroes and various life experiences; very few of which have anything at all to do with intelligence.

The enlightenment ideal of homo-rationalis has a sitting down before a table of facts weighing them in the balance pro and con and then employing logic and reason to determine which set of facts best supports this or that theory. This is not at all how we form beliefs.

What happens is that the facts of the world are filtered by our brains with the colored lenses of word views, paradigms, theories, hypotheses, conjectures, hunches, biases and prejudices we have accumulated through living. Then we sort through the facts and select those that confirm what we already believe and ignore or rationalize away those that contradict our beliefs.