the problem here is that very few people have been proven to be truly religious. most are like many of the muslim clerics in radical parts of the middle east today. they teach (often to illiterate people) that the religion says to kill anyone who disagrees, so what do these people do? they kill for that person. its a classic puppet/puppet master problem. the leadership who organize the death of people are rarely truly religious, they simply use religion to confuse and in some case blind people into doing what they want. in the end its all for power, religion is just used as a catalyst to gain support.
i can't really believe anyone would dispute that more deaths have been caused in the name of religion than none. as stated, mao himself is said to have been responsible for upwards of 50 million. hitler easily 20 million. stalin has numbers ranging from 20 million to 50 million. and so on and so forth. as previously stated, its all about power. heck, even in the bible you can see that with the pharisees. what they did was never in the name of religion, it was for personal gain, they just used religion to gain that power. there is a big difference