It popped up because of some sick psychologist, who abused children, wanted to prove that genders were not inborn but as a result of environment.
The medical community rallied because they thought it was a pathway to riches.
That is what is known, but there could be others who saw it as a pathway to destruction for Western civilization.
In very rare cases, kids have been brought up by monsters who raised them with the other gender. Culture is everything if some moron makes it everything. How to divide these from the people just making money off nonsense is the question.