fillippo
It's a way of legitimizing the whole thing, so e.g. rather than men saying "I want to be a woman", they can lean on this idea of gender identity and say "I am a woman", where "woman" has been redefined as "anyone with a female gender identity". And per the definition of gender identity, a man can be said to have a "female gender identity" if he wants to be a woman. Naturally, this redefinition has turned out to be quite controversial.
Parents of transgender kids sometimes allude to this too. For example, Susie Green, recently the CEO of the transgender charity Mermaids, said about her child:
> What I had come to the conclusion with [...], was that I had a very sensitive, quite effeminate little boy who was probably gay.
> [...]
> But Jack's dad did not approve of our child's effeminate behavior, and it created such tensions that we ended up in couple's counseling. We went to couple's counseling, and what they said to us as parents that we had to agree, no matter what it was that we agreed upon we had to agree. At that point, Tim decided that I must agree with him, apparently, and then all the "girl toys" or "girly toys" as such were taken away and put away, and Jack was made aware that this was not appropriate. And suddenly, a confident, happy little boy became quite quiet, withdrawn, very clingy, and tearful. I didn't like it, and I didn't think it was right.
Gay son, homophobic dad - and a mother who took him to Thailand for his 16th birthday to get his penis inverted and his testicles removed.