Quite right; the essential difference between left and right is the difference between ideology versus theology. Atheists by and large worship at the altar of State, Theists at the altar of God. The Left believes that power resides solely in Man, the Right believes it rests with God.
You have an interesting list there, but besides the Marxists/Communists, the only one I really associate with mass violence is the French Revolution. I thought most Americans regarded that as a "good thing", overthrowing monarchy in favor of republican forms of government has been very messy, but it has been part of the path of progress.
You are apparently unfamiliar with the Godfather of modern conservatives, Edmund Burke. His 'Reflections On The Revolution In France' draws a sharp distinction between the American Revolution and the French Revolution, ergo, their's was not "a good thing".
The other things you mention seem to be in the tradition of Europeans always wishing to fight each other over something, whether it be different flavors of Christianity, or Christians versus those who would throw off Christianity. If you want to judge atheists by the worst among us, then allow us to judge Christianity by its most infamous practitioners as well. Or, we could just both admit that social change in bygone years was accompanied by far more violence than Western civilization will tolerate today.
I disagree, it seems that an honest reading of history would show Christianity as a restraining force in civilization but once the"shackles of religion" were tossed off Western Civilization became exponentially bloodier and bloodthirsty, just as that famous atheist Freidrich Nietzche predicted it would.
The wars fought over the Reformation were not subject to the 'restraining force' of Christianity's message of 'love your neighbor', and I would submit that the fact that wars got bloodier and bloodier was a function of technology. The atom bomb that a Christian nation dropped on a Shinto one was the act that killed more people with one strike than anything else in history. Personally, I'm glad they did it, but Christianity is not overly connected in history with peacefulness.