Interesting that "psychotic disorders" can be replaced with "tribalism" and still be true. We can easily identify such false beliefs in other tribes but often have a blind spot for them in our own.
But in terms of tribes or politics it is not clear that this is a disorder. Believing the same false things as our neighbors is often rewarded with status, wealth and mating opportunities, while failing to do so can be deadly. What converts the same tendency into psychosis can be merely the context: it's psychotic to believe false things when there is no social advantage to it and it therefore becomes unfit. But the same is true of believing true things when they conflict with a tribe's deeply held false beliefs.
Like a propensity to violence, believing false things can be a deadly strategy. Or it can be the only strategy that allows a chance for survival. And you may not know which until it is too late. It would be nice to live in a world where violence and false beliefs are consistently maladaptive, but that isn't this one.