It's not about the outcome for this one individual. Even if they were magically able to predict their health in the future or to know that they've increased their risk of cancer, osteoporosis, etc.
Even if that individual were absolutely fine, which 'Lived experience' doesn't tell you, that doesn't mean it's OK to tell adolescent girls that the answer to their very normal and painful experience of growing into a woman Is to surgically destroy their body.
Very very few girls don't have these feelings towards their bodies as they develop. That's why self harm and eating disorders are so prevalent. And socially contagious.
The difference is that on the whole, parents, teachers, doctors and other authority figures generally try to reduce and stop those behaviours, not to encourage them and share in the belief that their bodies are disgusting and wrong and the answer is to hack them to pieces.
When i was anorexic, no one gave me appetite suppressants.
When i was self harming, they gave me stitches, not a knife.