You laugh, but here am I, an obviously failed atheist, in your estimation. I've never killed anybody. Stealing, molesting children, knocking over religious headstones and trashing churches, mosques, temples and synagogues are all things I consider to be wrong. I barely even swear, which a lot of people think is just a bit weird of me.
HOW COULD I BE SUCH A MISERABLE FAILURE? Oh, Shmogie, forgive me for not living down to your worst estimate of people who don't believe like you.
How I long to be as good as your Christian brethren like Greyson Fritts, a supposed Christian minister, positively screams for the execution of people like me.
See how easy it is? All you have to do is conflate "what a person claims to believe" (or not) with "what a person did" (or not), and then apply liberally to everybody else who claims the same beliefs (or not), and you've got yourself an ironclad prosecution!
The facts, unfortunately, are usually very, very different, and support almost literally none of the usual arguments. Humans act for human reasons, and while beliefs play a role, human beliefs are extremely liable to corruption by all sorts of corollary factors...like hunger, the lust for power, fear and hatred, misogyny, an excess of literalism, an inability to reason)n, an inability to empathize with others, and on and on and on...
What was the reason that Torquemada burned heretics? By is own claim, and by the claim of the Inquisition itself (still a major entity in the Catholic Church, only now called "Congregation for the Doctrine of Faith" for entirely religious reasons -- holding beliefs that were deemed heterodox. What was the reason that Mary Tudor burned Protestants? It wasn't for territory, or glory, it was specifically for to make her faith, the Catholic faith, the only one that could be legitimately held in her kingdom.
What was the reason for Stalin's purges? Did he ever, even once, make the claim that he was stamping out religion? How about Hitler, did he ever, even once, make a case for an atheist world view as his raison d'etre for the Holocaust, or for starting a world war? Nor, by the way, did he ever claim to be an atheist.
What was the reason for the French revolution? Was it because atheists (you mentioned Diderot and Voltaire and others) wanted to take control of the country and turn everybody into an atheist, or was it because the French were finally so utterly downtrodden and persecuted by their own rulers and the nobility that there was no way to stop it once it got going? Compare the French revolution with the nearly contemporaneous American one, which for some reason or other didn't seem to need a guillotine and lots and lots of blood. What was the difference? The difference was that Americans were already in a very real sense immensely more "free," had for more personal liberty, than the French could even begin to dream of.
This could easily become a Gibbon-length essay, but thankfully for all of us, forum rules don't permit that. But please, I urge you, when you try to make these kinds of arguments, try at least to make sure you are talking about what you really think you're talking about. If you think, for example, that Kim Jong Un, when he has someone executed, is doing it "because he is an atheist," then consider what the very devoutly Christian King Henry V was doing it for when he had someone executed. Perhaps, you see, it might be that the reasons turn out to be very similar, and religious beliefs might very well have had diddly to do with it.