The Nazis, on the other hand, are held as the embodiment of evil, almost unanimously.
Because the Communists won the PR war. Literally. When Stalin decided to denounce someone he called them Fascist.
It boggles the mind that any former Communist, an ideology that killed over 60 million people can be accepted just fine today and any former Nazi is forever considered the worst creature to have walked the Earth.
This is not to cry over some perceived unfairness to the Nazi, but rather to stand astounded that all Communists aren't being rounded up today with the same fervor. You claim to want justice for totalitarian perpetrators of genocide? Great, just don't pick and choose.