I am also interested in why people believe things. I think it's right to choose psychology for the first tag because I believe it holds the answer. People believe things because it gives them some psychic (mind) benefit. It's often easier to just join in with a group that you feel basically aligned to, than to dig deep and investigate all sides of what you're getting into. It can be easier and possibly even more personally beneficial to believe a comforting lie than an uncomfortable truth.