Jen nails it.

"How would you know?"

... [T]he advice I would offer to my children, and to my children's children:
Every decade or so, take a look around the society in which you live, and ask yourself if there is any group of human beings who are seen as something less than human. A big tipoff is if dehumanizing words -- terms other than "man," "woman," "child," "baby," or "person" -- are used to describe any category of people.

And if you ever see that going on, you might be in the midst of something gravely evil.

Yes.