The brains of trans people more closely resemble the brain of the gender the person claims to be. What more do you want, honestly? Do you believe that sex organs trump one's brain activity? One's inner mental experience of the self? The neurons firing in the brain that have patterns of the other gender? Should I just ignore everything that you say and call it illegitimate because it comes from your own mind? Your religion is all in your head so I guess I can just denounce that? You have no physical evidence of your god so I'll just denounce that? You have no physical evidence of your emotions so they don't exist. I guess sex is all about physical pleasure, instead of mental and emotional?
You have every right to denounce my faith.
Our brains are extremely malleable to the point where practically everything we do or don't do can change its activity.
For example, sugar and caffeine can completely change how the neurons in our brains fire.
A pessimist is going to have different brain activity than an optimist.
How much exercise, sleep and meditation we get can also affect how our brains operate.
This is not even touching the idea of suggestion that we are open to.
Basically - if a boy tells himself that he is a girl enough times - what effect would that have on his brain?
What if his parents and teachers are also telling him that he is a girl?
Besides - our brain activity does not justify anything.
Someone who suffers from depression or sex addiction will have different brain activity than you or me - but does that mean they are just destined to be depressed and addicted to sex?
There is never any reason to change how our brains operate?
It is much easier - and makes infinitely more sense - to change our brains than mutilate our bodies.
Because one is supposed to change while the other is not.