If we must compare every atheist leader to Stalin, should we not compare a religious leader with every other gods believing ruler from the entirety of human history? Religious leaders would include Caligula, Nero, Hitler, Atilla the Hun, Ayatollah Khomeini, Idi Amin, Leopold II, Vlad Tepes, Ivan IV, Oliver Cromwell, and the list goes on.
As it is only recently that any leader has dared to state their disbelief in god, we can ascribe all of humanities evil works over thousands and thousands of years to those who claim the existence of gods.