You are wrong about the Nazism. It was most political, but many were still Christians. The Nazi propaganda had mixed Christianity with a warped Norse/Teutonic myths. Nazism had peverted Norse protective symbols (Swatisfa) and Wagner's opera for their own imperialistic powers and greeds.
It is true that the Nazi's utilized pagan themes for nationalistic purposes. However, the Nazi party was blatantly anti-religious, and often oppressed or at least discouraged active participation in the church. The case in russia was even worse. An excellent study on methods and ideologies in Nazi Germany and Societ Russia is
The Totalitarian Party: Party and People in Nazi Germany and Soviet Russia by A. L. Unger (Cambridge University Press). More biased, but also more related to the anti-religious sentiments of totalitarian regimes is
Leftism: From de Sade and Marx to Hitler and Marcuse by Professor Erik von Keuhnelt-Leddihn.
What I am trying to say is that Nazism was religion-less, like atheism, so you can't really blame Hitler of being atheist.
Nazism was not religionless. The state became the religion (which is a form of atheism).
As to Communism of Soviet Union, atheism was just a tool to keep people oppressed.
Again, the state was the religion.
Interestingly enough, Freud's disciples (Jung, Adler, Reich) each found ways to reject his absolute denial of any purpose in life (Freud, in a letter to Marie Bonaparte, wrote Im Moment, da man nach Sinn und Wert des Lebens fragt,
ist man krank, and continues denn beides gibt es ja in objektiver
Weise nicht/(In the moment in which one asks about the
significance/meaning and value of life, one is sick, because in an
objective sense there is neither [i.e. neither exists]").
The point is that atheistic ideologies are just as capable of destruction and carnage as religious ideologies. More so, actually, but only because these ideologies were coincided with technologies which enabled greater destruction.
Do you blame Christianity for the dropping of two atomic bombs in two Japanese cities?
Although the US is based on Christian values, Christianity did not form an ideological background for a totalitarian government as with the Nazi party and Russia.
And then there were the witch-hunt for Communist sympathisers on American soils. Were they any better than the Soviets?
Yes. Far, far, far, less death and destruction inhouse.
No, on both account. US being a largely Christian in outlook, but many of politics behind it had nothing to do with religion.