You keep ignoring facts. The FACTS are that officially atheistic (as in, religion is against the law) governments have killed more people in the first half of the twentieth century than theocracies have killed in the entire written history of the world. That's fact. Or at least, it's certainly the well researched opinion of the man who coined the word 'democide."
Freedom, Democide, War: Home Page
Another fact: there HAVE been theocracies that were not especially murderous. There has never been a country in which all religion was made illegal that was NOT murderous. Not even one, beginning with the "Reign of Terror" during the French Revolution (though short lived and not complete, the attempt to replace Christianity and everything else with the 'cult of reason' got particularly nasty).
My point here is simple; yes, people can and do use religion to excuse killing. Getting rid of religion doesn't get rid of the killing. People simply use different excuses, and the one excuse religious killers do NOT use is "get rid of all religion in the name of reason!"
And THAT excuse has been used quite effectively over the last hundred or so years, I'd say that 'in the name of God" and "get rid of religion!" cancel each other out as 'reasons for violence," and certainly those who have been killing in the name of reason, or because they don't like religion, have been a great deal better at killing people than the religious have in at least the last two thousand years.
Shoot, they've been better at killing people than the sum total of government sanctioned mass murderers have been in the last two thousand years, 'in the name of God' or not.
That's not, as I have also written, because of 'atheism.' It's because people in power will do what people in power can do, which is pretty much anything they want. They justify their actions to themselves, and while theists can, and have, twisted their religions to justify killing people, they do have to manipulate an already existing belief, with priests that also have power and might actually restrain the leader, if only slightly.
Atheistic leaders don't have ANY sort of brake. No higher power to which they have to report. None that they have to make seem is on their side. They are utterly free to do anything they want, and whenever a leader was able to make religion against the law, mass murders..democide...happened. Every time.
I didn't come to this conclusion because I am biased towards a specific religion. I came to this conclusion because I saw the research and the sheer numbers...and who did the killing. My opinions here are data driven.
It doesn't matter much, it seems, WHAT religion is in play; it's better to have one, pretty much any one, than not to have one. Better still, there should be many of them. Even if they are entirely imaginary and false. It's better to believe that one must answer to something 'higher' to which one is responsible for one's actions than to figure that one is free to do anything one wants without personal consequence.
Secular humanism is atheist...but there is a 'higher power' to answer to for them; the human race as a whole. Secular humanists don't tend to be mass murderers. People like Mao, Stalin, et. al were not secular humanists.
But their personal philosophies were certainly atheistic. They had nobody. and Nobody, to whom they had to answer.