most people seem to be conveniently ignoring the main point of the OP.. i.e. that political movements based on atheism end up having to accommodate their version of heaven/paradise/salvation within space and time. To this end this gives them the sense that they have a kind of carte blanche to eliminate any obstacles lying in the path to this heaven on earth (the ends justify any means). if you're creating a kind of heaven then it's fine, and even a moral imperative, to crack a few eggs on the way, is the reasoning.
this helps to explain the extraordinary ruthlessness of such political systems in comparision to systems which place heaven/paradise/salvation outside of space and time (theism-based)
the fact that the 20th Century had better technology for killing people seems irrelevant to me. the vast majority of those killed by their own governments were killed with pretty old technology (hanging/shooting/famine-by-intentional-negligence/torture/gulags etc) Non-communist countries had the very same technology, but never indulged in the same level of criminality against their own citizens.
the population objection doesn't work either. in the communist era the total population of communist nations was always in a minority compared to total world population. yet they accounted for the vast majority of repression and murder of one's own citizens.
One last try, and then I write you off.
Scandinavian countries are overwhelmingly atheist, yet have the lowest level of violence and military aggression in the world. Why don't you mention them as an example of atheism? And since most of Europe was became quite atheist after the second world war, why don't you cite that as an example?
So, let's try this one more time, shall we? Communism is a dogma, a non-traditional religion. Communists believe in the God of History, Hegelian Historical Inevitability. Just because the God of another fanatic is not your God does not mean that he is not a religious fanatic. Just because the messianic figure that they hail is not your messiah does not mean that they do not share similar delusions. You are not comparing apples to oranges. You are comparing an orange to an orange and calling it an apple.
Communist countries were the
minority? China has a billion people!
The Holocaust was low tech? They used IBM computers to tabulate and track the inmates!
And finally, for Huxley's argument: naturalistic dictators may want to build their heaven on earth, but as I have already said (and you have pointedly ignored) so do Christian Domininists, Islamicists, and so did the every Christian sect four hundred years ago--each determined to convert the world to their faith. The one distinction is that for a secularist, there is no other world to escape to. Joseph Stalin understood that nukes could never be used. Osama bin Laden would use them in a heartbeat.
Consider a bus driver. If the bus driver is evil, he may drive like a lunatic, but he won't drive the bus off the cliff, because that would kill him too. But a religious fanatic has no such qualms. Heaven lies over that cliff. He will do it gladly. There is a bevy of lovely virgins waiting for him on the other side of that flaming wreck.
Kill them all! God will know his own!
They really do mean it.
And given the chance, they will do it.