Why do many of my fellow atheists deny the anti-theistism (Gosateizm) of the Soviets despite the evidence?

I don't, but atheism and even anti-theistism(did you make this word up? Cool.) aren't the reasons for the Stalin genocide as so many believers like to imply. The reason is political power plain and simple, and if Stalin took a page from the religion playbook and made the religious ones the bad guys rather than the non-believers for a historical change, I can't say I'm surprised it happened. Great question!