FUNDAMENTALIST is the key word there. Fundamentalists will do some CRAZY things in the name of their religion, and feel that they have the backin of God. Ever heard of the Crusades? Salem Witch Trials? Countless Jihads in Islamic countries? I can go on, but I think you get the picture. The fact is that while YOU may not see them as religious, they are in fact doing what THEY feel is right by THEIR God.
It's easy to just say, well, phhh, they aren't REALLY religious, they're just using it as an excuse. It makes it easier to assume that they'd be willing to work with someone they probably hate for religious reasons.