Yes, scary,
@Betty P, and it seems to be getting worse IMO.
I think your two ideas of "why" are both valid. Some kids are raised in it, probably going to meetings with parent/s and seeing, hearing and reading horrible propaganda, he-man or "you are superior" stuff, and learning to hate. Others may feel different from most of their school friends and perhaps bullied or embarrassed for their appearance, accent, lack of sports or academic participation, being a new student and being ignored, etc., so they seek something on the internet, etc. and find a group of kids who endorse this kind of thing.
They hear, read or see adults embracing such awful attitudes and feel like they have found something that makes them feel more important, and they feel like they fit in. And it just grows.