Their bodies get "fucked up" by hormones if they do nothing. We all get "fucked up" on hormones to some extent, it's just that puberty blockers allow more opportunity to decide which way to get "fucked up." If you truly wanted to help "brainwashed trenders" not "fuck up their bodies," you'd support puberty blockers. It gives them the most time to decide with as few side effects as possible.
You think transitioning is what happens when treatment fails? You think it's some sort of unfortunate outcome? The data paints a clear picture: transition is the best outcome for us. No other treatment works, and as far as treatments for psychological phenomenon go, it's one of the best.
I wish I could say you're dying on a hill, but you're not. You're throwing screaming children into a pit and burning them alive. You'll face no consequence for your humble contribution outside of possible guilt, but nothing will undo the harm.
If you people people on puberty blockers when they are going through development it will fuck up their body and they won't develop the way they are meant to.
Its not like it is reversible. If some guy takes puberty blockers from 12-18 there is no way he is going to develop in the man he would have without the blockers. Same for women. It stunts their development.
Ideally they'll start hormones or go off blockers by about 16, but you can't comprehend that because you already decided that 18 had to be the start point. You don't want trans kids lucky enough to discover their identity early to transition, probably not thinking through what the consequences are. You hope that they'll not medically transition, but in all likelihood, they'll just end up suicidally depressed for no good reason.
You're correct in assuming that gender isn't a choice, but incorrect in how you apply that idea. Attempts have been made to force cis boys that got maimed by botched circumcisions to be girls. They did not end well. Attempts have been made to find alternatives to gender affirmation, but they never work. Nobody can be converted. Nobody knows how.
Stop being a knob and accept the failures of naive doctors trying to snuff us from existence. You affirm us, or you torture us. There is no other option.