Earlier quoted context omitted.
I was under the impression that communism was centered around the notion that people are all equal and highly malleable, not that there were intrinsic and immutable differences between human groups. But assuming you are actually referring to nationalists (who probably rank #2 on the list of "worst things humans have done to each other"), I'll just quote a blog post Bryan Caplan wrote today: We've learned so much from…
Wasn't referring to nationalists specifically. I was thinking of the broad ranger range of things like slavery, genocide, segregation, apartheid, etc. If you think that communism is worse, that's fine by me. It doesn't change the fact that history is littered with cautionary examples of group-based determinism gone terribly wrong. It's naive to pretend otherwise.
"Meaningful variations between groups" does not logically imply that concentration camps are good policy, just as a belief in equality does not imply that gulags are.
Supposing that Jews are only half as smart as Aryans, it doesn't imply that they should be killed. Similarly, if I'm twice as smart as my maid, it doesn't follow that I should murder her. In both cases, you need some intrinsic moral belief that killing is acceptable - and that's where the real problem lies.
Also, need I point out that you are employing the logical fallacy of "appeal to consequences"?