Addicted To Partisanship

This explains a lot:

According to the research of Drew Western, political partisans -- and especially the smart, well-informed ones -- not only feel better when their brains downplay contradictory political information, they actually get a little emotional "high" when the brain (unconsciously) rejects evidence that contradicts their deeply held political beliefs. In a series of brain scans of political partisans asked to consider contradictory statements by the politicians they supported, Western found that the brain reverted to the comfort zone of its long-held biases -- and doing so actually made people feel good.