You mean the religious freedom to burn thousands of innocent women alive?
Or the religious freedom to shove nails into people toes because they're not convinced by the existence of a magical sky wizard?
Or what about the religious freedom to enslave the entire continent of Africa, or wipe out the Majority of Native Americans, or kill 6 million Jews in the name of God?
The reason why your argument is a joke, is because you're branding every go***mn atheists on this planet as a mass murderer just because a few psychopaths here and there just happened to be atheist?
Well guess what, their "atheism" was a anti-theistic personal vendatta, it had nothing to do with them being atheists. By contrast, religious bigotry, despotism and human persecution has been a solid cornerstone of human civilization since the dawn of man.
Your argument is absolute trash. Stalin didn't profess to kill in the name of atheism. He killed in the name of politics. The Spanish Inquisition, The Crusades, Islamists and countless other religious power houses, on the other hand, have explicitly stated that their actions have been in the name of God and Faith.