Religion is not for the truly smart people ( having an education or good memory doesn't mean you are smart), religion is for the dumb masses. The masses need a unified belief GIVEN TO THEM that offers answers to their questions. This is preferable to every clan creating their own local religion and then FIGHTING each other. You cannot have a society without organized religions due to this very reason.
Most people are stupid, meaning that they only know part of an issue after having read a book or reading articles on the internet. Even the simplest subjects have enormous complexities lurking beneath their hood.