I'm counting the dead not the oppressed ... atheists haven't been around long enough to rack up the same murderous numbers of death and destruction as theists have over the past few thousand years.

The Soviets and communist Chinese (both systems I disagree with and do not support) never launched full fledged pogroms, death camps or extermination programs of killing in order to get rid of religious groups .... they oppressed and abused religious groups and maybe even killed often ... but never to the level of industrial killing .. the Nazis did that and even though Nazis may be identified as atheists, they had a political / ideological belief system that was more identifiable as a religion than a lack of belief

The only system in history that has any blood thirst for killing opponents has been and still is religious based.