Communism as an idea has no inherent connection to those atrocities.

"The criticism of religion ends with the doctrine that man is the supreme being for man. It ends, therefore, with the categorical imperative to overthrow all those conditions in which man is an abased, enslaved, abandoned, contemptible being." - Karl Marx, Contribution to the Critique of Hegel's Philosophy of Right

Fascism and Nazism on the other hand are ideologies of inequality and annihilation.

That is not to say that you can't call yourself a communist and still be an enemy of humankind (so whatever kind of asshole) - but you don't have to be. But once you are a fasicst, there can be no doubt that you are.