Why?

Indoctrination gives you a worldview before you can question things. Its a vocal virus.

My mother left the christian church when she was 65 with the sentence "THese old white man don't have to tell me what i can do". And the context was a cousin of us coming out as a lesbian.

Yeah, probably "epidemic hysteria" (https://en.wikipedia.org/wiki/Mass_psychogenic_illness) or something similar might be more accurate, but that's also "a disease" of sorts, just mental/psychological rather than biological.