You're comparing apples to oranges here. The crimes you mention are all about subjugation of or violence against foreigners. Ill will towards foreigners is the human ur-prejudice -- it's older than our species, in fact. Giving in to this prejudice is something that could have happened under any politico-economic system. It happened under capitalism because capitalism is what we had then. If the world becomes a Marxist utopia tomorrow, and we travel to the stars, and find technologically underdeveloped aliens, it will happen then under Marxism too. It was certainly the case that the Soviet citizenry, however far advanced along the road to true communism they actually were, were perfectly happy to join the Red Army and oppress the hell out of the people of Eastern Europe for fifty years. And they did it they were told they were protecting the world from imperialism from the West!
The problem with Marxism that I'm talking about is much more specific. Communist leaders have a habit of liquidating populations that they deem insufficiently loyal. That's why Stalin killed the kulaks, Mao killed the educated middle class, and Pol Pot ordered the killing fields. Under capitalism there is no comparable tradition of massacring political enemies. And since political enemies are going to be a fact of life under any political system, thoughtful Marxists should worry a lot about how to protect them from the attentions of the state.