It might be worth considering that Sanderson grew up in the LDS church, which until very recently taught that being born white was a reward for serving God in a previous incarnation. Those who failed to serve God were born into other cursed races. The Native Americans were actually a tribe of Israelites who were cursed with their new appearance.
And many systems of slavery and prejudice have been 'justified' with the Curse of Ham concept, a reference to when a character in the Bible gets cursed so that all his descendants will be servants and menial laborers. They decided that it clearly meant black people. Other times the concept was Manifest Destiny. Basically "Here we are conquering this place, clearly God thinks we ought to have it."
This isn't so much a thing Brandon does, as a thing Brandon recognizes as a pattern in cultures. People don't like hurting other human beings, so dehumanizing others is a requirement for certain types of civilizations to function. Everybody has done this, they come up with reasons that their hate and suspicion are correct, it's never justified.