http://en.wikipedia.org/wiki/Cognitive_dissonance
This could be the explanation of fundamentalist religion. When people claim to believe things they know is not true, it causes the mind to form reactionary, defensive mechanisms.
Even Creationists know that the world is not 6000 years old. But, their cognitive dissonance causes them to disregard their better knowledge. They know that evolution is the real explanation for biological diversity, but this mental condition makes them adamant in their protestations nonetheless.
This could also be the reason why so many formerly religious atheists feel such a joy and relief when they abandon religion. They also abandon cognitive dissonance. It must be a lot of upkeep.
DF