Innate

If there were no biology involved in gender identity, David Reimer would not have reverted to living as male when given the news as a teen of his reassignment after his botched circumcision. John Money would have been proven correct that gender is a social construct; something which TERFS espouse as doctrine. If they allow for the possibility that transgender people are not deluded, it destroys their dogma that men and women have no differences other than physical ones. 

As it turns out, Money was indeed wrong.

Of course every process on this planet is nuanced and even if feminine natures are largely found in females and masculine ones in males, it does not mean it is exclusively so. Within the sexes there is a spectrum of masculine and feminine such that the more one examines in detail, the more fragmented the socially imposed binary appears.

Of course agendas are everywhere which is why nuance is glossed over since it is often highly inconvenient; certainly thick-skulled conservatives who worship black and white have problems with it.  Even within what today is termed the "trans community" there are motivations, behaviors and identities which vary by virtue of the size of the large tent created thereby watering down the efficacy of the descriptor. It's one of the reasons I pay less attention to nameplates as they don't tell me enough.

That there are brain differences in people which affect self perception should be unquestioned and we can argue for innate inclinations at the same time as not using them to discriminate against anyone.

                          John Money