Obviously, what is in the mind can be different from what consists the body.
If a man loses an arm, he will miss it. It was his arm. In his mind, he feels the arm he lacks. He wants his arm. Arm is still part of him in his mind.
Now, if a girl loses gender and gets born in wrong body, I cant think why would anyone be upset by the idea that she calls herself a girl.
Like, it doesnt affect you. What do you have with her?
Why exactly do you care?
Now, if someone is trans species, trans age or trans race, it is same.
I dont see why you feel the need to control someone's private life.
Remember that old poem?
First they came for the Communists
And I didnt defend them, because I was not a Communist
Then they came for trans
And I didnt defend them, because I was not trans
Then they came for homosexuals
And I didnt defend them, because I was not a homosexual
Then they came for the Jews, the migrants and the atheists
And I did not defend them, because I was not a Jew, nor migrant nor atheist
Then they came for me
And no one was there to defend me.
What is important is unity. As long as people are united, they are much stronger than when divided.