I can get you to think of people—even a group of diverse-looking people of both sexes and all ages—as a kind, by making generic remarks about them. And you’re more likely to accept a generic claim about a group if what it says is something negative or worrying. We humans are more likely, then, to essentialize groups about which we have negative thoughts; and more likely to have negative thoughts about groups we’ve essentialized. There’s an unfortunate vicious circle for you.
