Most "Christians" have arrived at their present state of belief not due to independent thinking, but to being brainwashed as children. Ask them their reasoning behind one of their particular beliefs and they will either say something completely bonkers, refer you to their pastor, or quote from the Bible.

Almost every one I've met is a self-righteous, hypocritical, holier-than thou ignoramus who inevitably has a stunningly flawed and skewed view of the world around them.

Historically, Christians have been responsible for unbelievable amounts of violence and murder in the form of wars, crusades, etc.

There are lots more reasons I could type, but I have to take a shit and shower before work.