Not even close to debatable. The most wildly optimistic estimates for religious murders is slightly more than 1.5 million. There simply weren't that many people out there to be murdered for one thing. Stalin alone is responsible for between 35 and 60 million. Mao another 150 million, and we would be remiss to not include Hitler and his 5 to 6 million. Pol Pot 2 million, etc.
So no. Atheists are the most murderous group this planet has ever seen.
Incorrect on most of it. Hitler was linked at the hip with the Catholic church.
More importantly, what good is any religion if at ANY time it results in the murder of millions of people? We are to judge whether a religion is worthy if it has murdered less people than someone else?
Bizarro world. Which is the domain of religion.