To take it to the extreme, us-vs-them-good-vs-evil seems to be one of the biggest basis of most large scale oppressions ("the jews/blacks/muslims are less than us, less than human. it's us vs them."), and it facilitates the justification of war and the entrenching of religious bigotry through subconscious (and sometimes conscious) dehumanization.
I know I took your post off topic and to the extreme, but it just doesn't seem like a good mentality to grow up with. Thoughts?