actually nazis just wanted to conquer Slavs and make Jews dissapear, because they were a threat to them. Hitler just wanted the Jews out of his sphere of influence, he was thinking of sending them to Siberia or Madagaskar. Only when he realised he couldnt just make them dissapear, he proceeded to mass killing, which drained him of money, soldiers and resources. Can the same be said about Stalin and Mao? No matter what the answer is, doesnt really matter.
If Stalin and Mao wanted to kill civilians they wouldnt spend billions of dollars on developing infrastructure, schools, hospitals, roads, railways in their region. Nazis didnt build in the regions with non-Germans.
Central Asia had nomadic muslim tribes for centuries, their economy was based on goat trade. Communists raise their standard of living for 30 years (one generation) and Tajiks, Kyrgyzs, Uzbeks, Turkmens and Kazakhs became doctors, teachers, pilots, cosmonauts, military officers, generals. Central Asia vote 95% to keep USSR in 1990 when they had referendum.
Communism as Capitalism, succeded in some parts of the world while in the other, failed. And as we have proof of the last 20 years, Chinese style Socialism might be the best we invented in human history (until we test venus project's resource-based economy). Because one party system maintain order while capitalist mode of production develop economy. Soviet Socialism failed because it collectivized economy but one party did maintain political and civilian order, while Western Capitalism develop economy but fail to maintain order among civilians.