Atheism is not an ideology, therefore it is not possible to kill in the name of atheism. Religion, however, doesn't have the same benefit, and was in fact responsible for a great number of wars all throughout history.
Atheism might not be an ideology but atheism can be used to develop an ideology. As such, atheists can be , and hav been, responsible for the massacre of millions.
Democracies are based on "majority rules", more or less. Those "less religious areas" include areas where atheism is the majority (these areas also coincide with the "best" countries in the world, FYI). The events you have described only occurred in situations where the atheists were "all-powerful" - dictatorships. "Power corrupts; absolute power corrupts absolutely".
I don't know what you're reasoning, here, proves. Theists hold a huge majority in this democratic republic, but, I don't believe atheists have ever been singled out for extermination. We're both agreed that, in democracies, this type of thing does not gain official sanction. I agree with you that "absolute power corrupts absolutely". And I would admit that there are theists, in this country, who would love to gain that absolute power. If so, these would certainly do all they could to eliminate the opposition. I happen to know more than a few of these. I would hope, on the other hand, you would agree that there are atheists who would love to gain enough power to outlaw religion if it were possible.
You are correct in saying that atheists can be just as cruel and inhumane as theists. But that has no connection to their (lack of) belief. The theists' inhumanity and cruelty, however, do.
I won't argue this point but I believe my arguments, here, have been directed to a poster who implied that we wouldn't have "witchhunts" if atheists were in control.
I've read many books, written by atheists against religion, and some have suggested that religion is a threat to humankind that ought to be eradicated. They could be right. Religious belief might be detrimental, in the long run, to society. But you see my point. If atheists had total power of any government, they might be just as intolerant of religion as religion has been.
It has always been my understanding that the vast majority of atheists who state that theists' beliefs (religion) are detrimental and should be eradicated does not extend that to the theists themselves.
I would agree but, if my memory serves me correctly, it seems as if Harris gets close to it.