This is why if you have a neighbor, coworker, family member who is insistent on red-hat propagandizing, but seems "otherwise normal," they ARE.
But they have gone increasingly far down a SOCIALLY reinforced path of wacky and harmful irrationality.
The danger of labeling this membership a sign of "mental illness," is we will be unprepared for many "normal" and "nice" people we know to support and even engage in hateful and violent acts.
THIS is what is meant by the "banality of evil."