Not defending racism, but how I hypothesize that it happens is as such: People exist in one dynamic where it is accepted and are introduced to another dynamic where it is not tolerated. This leads to a push pull between both dynamics, where the person is constantly questioning which behavior is correct. If the individual thinks about this, and thinks themselves an individual, they may behaviorally react at the constant attempts by others at forcing a definition of behavior or control over the individual.
It's not really fair because neither dynamic has provably defined a correct way of handling social situations/definitions/behavior, because both behaviors often can be traced back to some kind of "reasonable" adaptation or "successful" adaptation which, when not confronted by an equally successful/reasonable force, can become exaggerated,distorted (not necessarily in a bad way).
The problem is some people can explain themselves in a socially acceptable manner, and others can't. People with schizophrenia are some of the least likely to be able to verbalize themselves without the fear perception that it will be taken seriously, equally, diligently - if only from traces of memories of prior experience. People with paranoia have difficulty trusting anything, whether it's the meaning of a word or the person they are talking to. Their minds operate on a different level that is disconnected (not necessarily in a bad way) from people who regularly socially engage with a reasonable level of social connection. If you can't think like a schizophrenic, how can you possibly expect them to be able to communicate themselves in a way that you can empathize with, without them accidentally forcing their own distorted fears onto you?
If you had to question every post you made assuming two worlds exist: one in which the post affects you positively and one in which the post affects you negatively, and you can't tell the difference between either because the possibilities of how reality can manifest are too numerous (or too obvious) to think about, you would constantly be stuck between deleting half your posts and posting things you aren't sure you believe. That's enough to make anyone a little crazy, simply because of the resulting ways that influences your thinking.