Probably because they were raised to uncritically believe that MAN IS WHEN PENIS AND WOMAN IS WHEN VAGINA is some sort of One Universal Truth™ so they are terminally stuck in their 1950's understanding of the world, and anything that challenges that One Universal Truth™ must be derided as some kind of "mental illness" because clearly our understandings of biology or sociology or any other anthropological field are incapable of being updated over time, because that would mean they would have to actually learn something new, and god forbid they try to learn anything new beyond grade school.
Worth remembering that the overwhelming fanatical obsession with trans people is only a few years old. Before that it was gay people, before that it was "Urban youth", and so on and so forth. They can be re-trained to switch to a new target in less than a year.
Probably because they were raised to uncritically believe that MAN IS WHEN PENIS AND WOMAN IS WHEN VAGINA is some sort of One Universal Truth™ so they are terminally stuck in their 1950's understanding of the world, and anything that challenges that One Universal Truth™ must be derided as some kind of "mental illness" because clearly our understandings of biology or sociology or any other anthropological field are incapable of being updated over time, because that would mean they would have to actually learn something new, and god forbid they try to learn anything new beyond grade school.
Worth remembering that the overwhelming fanatical obsession with trans people is only a few years old. Before that it was gay people, before that it was "Urban youth", and so on and so forth. They can be re-trained to switch to a new target in less than a year.