It's because a large percentage of Christians read the warm and fuzzy parts of the New Testament, glossed over Jesus hulking out on street vendors defiling the temple, and completely skipped the Old Testament's rules, enforcement thereof, and smiting of evil that's required as the basis for a functional society. It's akin to reading the "How to fly a plane manual" and skipping the first half where they cover takeoff so you can go read about the in-flight cocktails. It's a good way to get yourself killed.