Religion has little to do with this stuff. If such people weren't using it as an excuse for their evil then they would find another one. Islam and Christianity is neither good or evil or anywhere in-between they are simply belief systems. The good or evil comes from the people who follow them, they are the ones who decide what those belief systems mean to them.
I don't think I agree with this. If these people weren't indoctrinated by ridiculous make-believe stories, then they wouldn't be doing this. You can dress it up all you like, but it IS about religion.
People aren't using it as an excuse for their evil, they have been made evil by people who interpret religion in such a way.