This is why George W. Bush is so clear-eyed about Al Qaeda and the Islamic fundamentalists. He believes you have to kill them all. They can't be persuaded, that they're extremists, driven by a dark vision. He understands them, because he's just like them ... This is why he dispenses with people who confront him with inconvenient facts ... He truly believes he's on a mission from God. Absolute faith like that overwhelms the need for analysis. The whole thing about faith is to believe things for which there is no empirical evidence ... But you can't run the world on faith."
From this piece in Salon about disillusioned right-wingers, who may be bad, but not actually mad.