Religion does nothing but create conflict over things that do not exist. In a perfect world religion would exist solely to teach one morality and virtue...but it can't even do that since most religions have vengeful deities that hand out severe punishments for crimes such as "Believing in the wrong version of them". Now that science can explain most of the "unexplainable" things that people created religion to explain for them I think we should just let those beliefs die. We'd be so much better off without Muslims blowing themselves up on every continent because they think the Great Not-There will be pleased. Or if the Inquisition and Crusades hadn't destroyed a fuck ton of knowledge and culture. Or if the Holocaust hadn't killed 6 million people (although that wasn't entirely religion's fault).
Murders committed in the name of religion: Probably hundreds of millions
Murder Committed for Atheistic reasons: Still high but I bet it's less.