History is distorted when brutal dictators are labeled humanists. While atheism is no sure barrier against moral atrocities (since it’s simply a lack of theism) if leaders use their power to engage in an aggressive campaign of war and atrocities, they are by definition, not humanists.
Adolph Hitler was a Roman Catholic, baptized into that religion-political institution as an infant in Austria. He became a communicant and an altar boy in his youth, and was confirmed as a "soldier of Christ" in that church. Hitler seeking power, wrote in Mein Kampf, "... I am convinced that I am acting as the agent of our Creator. By fighting off the Jews. I am doing the Lord's work." Years later, when in power, he quoted those same words in a Reichstag speech in 1938. Three years later he informed General Gerhart Engel: "I am now as before a Catholic and will always remain so."
Hitler never left the church, and the church never left him. The church banned great literature but Mein Kampf never appeared on the Index of Forbidden Books. He was not ex-communicated or even condemned by his church during his lifetime. Popes, in fact, contracted with Hitler and his fascist friends Franco and Mussolini, giving them veto power over whom the Pope could appoint as a bishop in Germany, Spain and Italy. The three thugs agreed to surtax the Catholics of their countries and send the money to Rome in exchange for making sure the state could control the church.
Hitler's Germany merged state with church. Soldiers of the vermacht wore belt buckles inscribed with: "Gott mit uns" (God is with us). The priests often sprinkled his troops with holy water. It was an officially Christian country whose citizens were indoctrinated by both state and church to blindly follow authority figures, political and ecclesiastical.