I hear that Mao only killed a couple dozen of his own people.
See, that's the thing. A central characteristic of the communists is to accuse their enemies of what they themselves are actually doing. While the Soviets were actually committing intentional mass murder of their own population (prior to, and during the war), they were putting out massive amounts of propaganda about the Germans doing that. After the war, that propaganda was deemed by the victorious Allies to be useful for advancing the anti-German policies they had planned (see, e.g., The Morgenthau Plan), so they adopted and promoted it themselves, and codified it at Nuremberg.
