Why do so many people justify their hatred with religious rhetoric?

Before anyone says "Why do you think all religious people are hateful!?", let me make it clear that that is NOT what I said. I asked why SO MANY people do, not everyone. I know a great many people who practice their religion the best they can and try very hard to be accepting of other's opinions. My question is, how can some people justify hatred and bigotry with a book they can't prove is accurate, or by quoting their preacher's opinions? Do they not see the conflict in this "logic"?