For everyone interested: That fount of wisdom, Wikipedia, has a useful set of citations describing Hitler's intentions to destroy or alter German Christianity: http://en.wikipedia.org/wiki/Religious_views_of_Adolf_Hitler#cite_note-Bundle-3
Hitler talked of his faith in Christianity because he was good at tailoring his speeches. If he was talking to a mostly Christian nation, he would sound Christian. Doubtlessly he encouraged pagan-oriented and anti-religious supporters the same way, if less publicly. The main goal was in all things to subsume society to his own wishes.
Putin, pointing to individual examples of the Greeks or Romans is beside the point, although I still do think you're mistaken - the number I have heard (can't find the citation, but it is my lecture notes) is that he was responsible for the execution of over a million people, not counting battles. The Roman empire was most decidedly a slave economy, and while it was fine for educated slaves in classical Athens, it wasn't quite as nice for the ones working in the mines, or the huge numbers of slave kept in Sparta.
"Rome was quite generous to those they conquered, turned them into autonomous client states, and even paid tribute to their gods." That's rather cold comfort - Julius Caesar kills thousands and thousands of Gauls, literally solely so he can get more political power back in Rome, and the alleged generosity of imperial subjection is their reward? And if things were so generous and everyone so happy, why did the Romans bother to pay for all those expensive legions in their conquered territory? But anyway: Your big picture division of the world between the humane classical era and the cold and wicked dark ages of theistic hegemony lacks historical basis.