I may be wrong, but I seem to remember that this is a major point made by Michael Parenti in “Blackshirts and Reds” as an example of counterintuitive anticommunist propaganda. Effectively, the nuanced details of the Nazi atrocities are pretty widely known, for example, Göring and Himmler’s roles as “architects” of the final solution compared to Hittler. By reducing public awareness of the specific and personal details of atrocities committed under communist governments, criticism sort of bleeds across to the ideology. Any discussion about the specifics starts to become implicit apologia for tyrants, which makes propagandising against it easier.

Another example is while It’s common knowledge that Hitler was democratically elected, it’s not nearly as well know to most people if Stalin was. Drilling into the specifics, including his personal dismantling of democratic systems, would require a little too much examination of communist ideas (like that the word Soviet means “worker’s council”).

I haven’t read much Parenting so please feel free to correct my understanding of his points.