Thinking "Finland doesn't exist" or "Dinosaurs didn't exist" is "Dangerous to yourself and others". How?

I always thought the same thing about racism or sexism. Nothing but heresies. The average person being a little racist (if you can even define what that means) is the natural state of being and doesn't hurt anybody. If you're black and some white person says he doesn't want to be around black people, so what? You should be happy he was honest about it instead of pretending to get along and stabbing you in the back later.