The 20th century was created by idealism. Communism and fascism and Nazism are all based on idealized systems, what the world should be ideally, and how it isn’t what it should be, and therefore we’re entitled to change it radically and take control of it in order to do so.
One of the primary questions, or problems as I see it, is this “illusion” that sameness will bring safety. People start to thinking that if we are surrounded by similar people, like-minded people, if we have communities based on sameness, that will bring us safety. That’s an illusion. That’s not the case at all.