I think that part of the reason the Third Reich was so scary was that they made a legitimate claim to authority before following their program of persecution. I think it was the element of legitimacy- that they had the power to say it was right that they do what they were doing. Overpowering and exclusion after all were not new, but I think the fact that it was couched in (and accepted for so long) as institutional policy of a legitimate state was the more horrific and indefinable fear producer. Related to that was the expectation then that if an individual too was supposed to be legitimate they should also follow the policy of exclusion or be deemed illegitimate themselves.
I was also thinking about the attempt to create social boundaries (in the sense of demarcations between groups). I think that Realists (and certain party hacks I know) believe the only way to ensure that you get what you want or need is to divide the population into groups and make sure your group has more power (soft or hard) to the extent that the other group(s) can be subjugated to your will. The issue is that those divisions are always constructed and ostensibly (with enough power) can be deconstructed.