I used to think that believes really don't matter as long as the person doesn't act on it, but almost all believes shape who we are. It starts with little comments and evolves into actions. It doesn't have to be that way if people acknowledge harmful ideas, but if you let someone believe that women are worthless or that their race makes them superior for long enough they will become a bad person.
Before 2016, for example, we used to ignore a lot of conservative blustering as just political posturing or not worth attention because they could never do anything about it. Then Trump takes office and suddenly everyone with these shitty beliefs feels empowered to act on them.
People who have shitty beliefs are just waiting for those beliefs to be validated by someone in power so they can quit masking and act on them.