And here's your head.
Killing in the name of atheism explicitly is very rare. Killing in the name of religion? Not rare. The communist regimes of Mao and Stalin killed for political reasons, not religious ones. They may have happened to have been atheists (although, I'd argue they thought of themselves as gods), they did not kill to promote atheism. Meanwhile, you have things like the Salem Witch Trials, the Crusades, September 11th, ISIS, etc. literally killing in the name of religion. 'You don't believe as I do therefore you must die.'