The source of all human evil is a lack of consideration. Talking, and talking with new people especially, is the best way to encounter novel perspectives. If you encounter enough new perspectives then through sheer dumb luck some of them might be actually relevant to the choices you need to make.

To be honest, I have no idea where you got your conclusion from. But if it really is an issue with human nature, and you really do have examples of this happening in the past, then I would like to hear more about your take.

Can you name one of these horrible things that happened in history and where the people might have gotten their beliefs from if not the authority?