It’s not like people, especially anarchists, somehow didn’t notice that people can sometimes be awful to each other.

In my experience, many people who follow an ideology or who have some deluded conception of reality or humanity believe that people will cease being awful to each other when some specific better future comes about. Communists with the revolution, Christians with the return of Jesus, deluded “spiritual” people with the New Earth or “new age” people with the Age of Aquarius and even, dare I say, some anarchists with non-hierarchical society.