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 human genetic research. But when I read Fisher, I understand why the subject terrifies so many people. Hereditarianism combined with inane, half-baked moral philosophy does indeed logically imply Nazi-style homicidal mania. But don't blame the facts of human genetics. Blame the inane, half-baked moral philosophy.
http://econlog.econlib.org/archives/2012/01/the_demented_pa....