If we are talking about ex-USSR, the very popular among ignorami there idea of mental disorders is that these are not genetic like albinism, but something infectious like HIV, or a conspiracy by psychiatrists, or some other crap.

It’s stigma combined with fear. Well, and also the fact that in USSR only people with really debilitating conditions, like schizophrenia in full cognitive decline stage, would be hospitalized, and usually forcibly. And, of course, another category of patients - political dissidents diagnosed with a specifically invented type of schizophrenia to lock them up.

EDIT: Ah, and also that weird idea that people with mental conditions are always in everything less intelligent than people without those. Say, when you are autistic, people often outright refuse to understand what you say, until met with reality. References to stoicism or common ideas that Einstein or some Roman emperors or someone else very probably were autistic, or, say, Anthony Hopkins, and who not, - these are all in wain until they retrospectively see you were right.