Often when critics of religion like Richard Dawkins or Christopher Hitchens mention the amount of blood - and its a lot - spilled in the name of some god or another through history, the religiously inclined retort that atheism has wiped out its fair share of people as well. Nay, they say, atheism has killed MORE people because the greatest butchers of all time, the dictators of the 20th century such as Hitler and Stalin massacred people on a scale that religious atrocities such as the Inquisition never had a hope of approaching. Ergo, they argue, atheism is worse than religion. Religion might make some people behave badly, but atheism is much much worse.
It's a curious argument to be sure. It both misses the point of what thinkers like Hitchens or Dawkins are saying and is, for the most part, wrong - particularly when it comes to idiots like Stalin and Hitler.
Firstly, what Dawkins et al are saying is this: Religion doesn't, at the end of the day, make anyone behave any better than they do without it. On the other hand, because most religions draw stark lines between believers and non-believers, and often is extremely hostile toward non-believer to the point of utter condemnation, religion provides an easy justification to harm, perhaps to the point of killing, other people of different points of view. The Inquisition is justified and motivated by faith. The nuts who kill abortion doctors justify their murders through their faith. The 9-11 terrorists and the entire Islamlist Jihadist world view is motivated by and justified by their faith.
Now by the same token, you never hear of an atheist blowing himself up in a pizza shop or crashing a plane into a skyscraper and the like. The reason is because atheism is not a belief. It has no codes or creeds. It has no priests, pastors or popes. It has no bibles, scriptures or commandments written on stones. It has no organization at all. There is no atheist code that says someone should be stoned because they don't believe in god, or who they sleep with, or for working on a Saturday or Sunday.
What atheism is, all atheism is, is someone saying they will not believe something for which there is no evidence. Period. Atheism by definition provides no justification for killing anyone for any reason at all. There might be a justifiable reason to kill another person such as in self defense. But that has nothing to do with the intellectual position of not believing in an invisible, supernatural god or gods on the say so of an ancient book without a shred of evidence.
So whereas religions often provide explicit instructions on when and how to murder someone - just read up your Old Testament for instance - atheism provides no such justifications.
So, that said, when the religiously inclined say the worst horrors in history committed by Stalin and Hitler are the horrors committed by atheists, because they are atheists, do they even have a leg to stand on?
No. They assume, incorrectly, that atheism must have the same kinds of rules about how, who and when to kill as their own religion does. And they make a further mistake by labeling Hitler an Stalin as atheists in the first place.
First lets deal with genocidal moron #1 - Adolf Hitler. Was he an atheist? Nope. Hitler was raised as a Catholic, but would end up rejected Catholicism. However, he believed in God and Jesus often referred to himself as Christian - although his Christianity was something most Christians I know would not , thankfully, recognize as their faith at all. Nevertheless, what this loony advocated was a Nazified version of Christianity sometimes called "Positive Christianity" which saw Jesus as an active fighter against Jews. This sort of intense anti-semitism was in vogue not just in Germany, but all over the western world at the time. Hitler used this as part of his justification for his insane "final solution". It also served as part of the whole Nazi thing, in which their nationalist nonsense took on a religious life of its own - complete with blind faith and obedience to a higher power...only in this case, the higher power was a ex-house painter with a lousy mustache.
It would be, I think, incorrect to say Hitler did what he did solely because of his religious beliefs. But it is totally incorrect to say that Hitler was an atheist. He was religious.
Now, genocidal moron #2 - Joesph Stalin. Was this comrade an atheist? So far as I know, and I stand to be corrected, yes he was. However, did Stalin do what he did because he was an atheist? Nope.
Compared to his one-time Nazi ally, Stalin's actions and attitudes toward religion are more complex. He was utterly hostile to organized religion and went after the Russian Orthodox Church with a zeal that would chill Chingis Khan, (but as a sometimes pragmatist, he let them alone during World War 2 because they were a "patriotic organization"). The question is why. Atheism has no creeds or codes that could be used to justify his actions. Rather, Stalin's violence was in part a result of his nutty paranoid personality and the repressive nature of the Soviet government that he, along with Lenin before him, had built.
The USSR under Stalin was, like Nazi Germany, a hyper-nationalistic state (created so by lethal force). The state had to replace religion because the only loyalty could be to the state - and what's more, that state had its leader to which you had to totally loyal and obedient. It was cult of personality. Stalin's face was everywhere from photos in classrooms to huge paintings in public places. Stalin was destroying religions, in part, as a way to wipe out the competition. He needed Soviet citizens to be loyal to him and him alone - not to Jesus or Buddha or Mohammad. Undoubtedly, that he didn't personally believe in any of the teachings of the religions he was crushing helped the process along...it is must easier to destroy something you have no stake in after all. But his justifications, rooted as they were in the cult of personality he created and the whole Soviet communist philosophical clap-trap, underpinned his actions, not his unbelief in god.
At the end of the day, the term "atheism" might not even properly apply here. What he created was not an atheistic state. Stalinism was the state "faith". He created a Stalinist state using ubiquitous propaganda, a personality cult and secret police to establish himself as an absolute dictator. Stalin was not so much an atheist as he was the ultimate Stalinist. (Although he never used the term to describe himself. He was an "Marxist-Leninist", he would have said, and like Nazism, the whole Marxist-Leninist dogma required a complete surrender of yourself to a idea unsupported by evidence...just like in most religions.)
Both the Nazi and Stalinist regimes had all the hallmarks of a religion, and were not particularly atheist states at all. They both created a culture that crushed skeptical inquiry - the only true hallmark of atheist thinking - and enforced blind obedience and loyalty. To question the state, was to question the truth of the world as these governments defined it...and to deny that was to forfeit your life. The only reason their death tolls were of an order of magnitude greater than the religious atrocities that came before them was not because Hitler was not a "proper" Christian or because Stalin didn't believe in god. It was because Hitler and Stalin had access to technology that simply hadn't existed before.
Consider what the Inquisition would have been capable of if they had guns, tanks, gas chambers and other 20th century tools of death. It's a sobering thought.