The problem with Communism, Naziism, and Theocracy is a top-down attempt at creating a preconceived utopia which is inevitably at odds with the organically evolved social, political, and economic order. Recent excursions into this have been far more devastating simply because of advances in technology, particularly in the technologies of information exchange and weaponry. The theocracies of the past did not lack the intent, simply the means, to wreak havoc on this scale.
To see that that intent still exists within the theocratically inclined, read the ravings of Dominionist Christians or Islamicists. And while even Joseph Stalin understood that nuclear weapons could never be used (and was terrified of them), you can rest assured that if Mohammed had had the bomb, we would not be having this conversation. Why preserve this world, when God, or Allah, is just going to make you another?
What you must understand is that Communism and Naziism occupied the same social and ideological niche as religion--they were dogmas. Communism was called The God that Failed, where children were told as late as the eighties that "Lenin is the friend of all little children." Note the present tense; Lenin was stuffed and mounted in Red Square, and was not in a condition to by anyone's friend--certainly not by the standards of dialectical materialism. Hitler established The Church of the Reich, open only to party members, with his picture above and a copy of Mein Kampf upon the altar.
As the Church of Scientology (and Heaven's Gate, etc) demonstrate, you don't have to mention God to create a religion. The real danger, common to both religion and recent political ideologies, is dogma, an unreasoning certainty that you are right despite all obstacles, evidence, and costs to others, and that you can impose by sheer force a new and better order. Atheism, however, is not a dogma, nor even a belief, but a rejection of a particular dogma. Huxley got it completely wrong here.
