I'll add my opinion on this Atheists part. Some religionists sometimes kill and claim it was in the name of God, but Atheists never killed in the name of no-God, and if they did kill in the name of no-god, they never said or made it public that this was their motive.(As far as i'm aware)
So if some Atheists did kill in the name of their atheism, their is no proof for that because they never claimed that they did it for that reason. Which is not the case with some religionists or Theists.
Not only is there no proof, it doesn't make sense in the first place.
"Atheism" is no more a religion than "theism" is. Have you ever seen any theist who's willing to kill for belief in god(s) generally? Was there ever a bloodthirsty, religiously-motivated conqueror who would kill all atheists, but spare all the theists... even those who disbelieved in
his God(s)? That's analogous to the idea of an atheist who would kill for atheism.
Many, many people through history slaughtered huge numbers of people to advance their worldviews. Some of these worldviews were theistic; some were atheistic. In all cases, though, the point was to advance the specific worldview, not to advance theism or atheism in a general sense.
Stalin, for instance, didn't just kill the religious. He rounded up freethinkers, political opponents and all sorts of other atheists in his progroms, right along with the religious believers. He was just as opposed to a range of atheistic beliefs as he was to religious beliefs.
I personally think that some Atheists leaders kill out of their hate for religion, but i don't have a proof for that.
In a sense, I'd agree with you. If a tyrant wants to force a belief system on his people, then religions are competing belief systems that would get in the way of this.
Still, though, I'd say that the vast majority of modern atheists are also secularists, humanists, or freethinkers and are opposed to forcing
any belief system on people. When people pull out the old "Hitler/Stalin/Pol Pot/etc. was an atheist" line as if it's supposed to apply to their belief, I think that all it really shows is the person's ignorance of what the atheist he's arguing with actually believes.