I think your understanding of how people form beliefs is not accurate.

Both good and bad ideas are contagious. Humans are vulnerable to social proof. Most humans aren't that smart. Most humans aren't impervious to the madness of crowds. They will adopt the religion of their parents. They will adopt the bigotry of their peers, typically no more and no less. A person from 100 years ago is more racist than a person today because they were surrounded by different norms. People aren't rational actors, they absorb what they're given.