It's not just "chopping of healthy flesh." It's a professional surgical reconstruction of the male chest, and it's been proven to benefit the lives of transmen. Trans kids aren't the ones receiving this surgery, it is near impossible for them to even be able to get as far as a consultation with a surgeon. Telling someone with anorexia to get liposuction or that they are right about their deluded feelings is a false equivalency in comparison to a transman getting top surgery. It's really hard to get a referral for top surgery, it takes at least 6 months of gender therapy first, and the waiting lists are unbearably long. The difference is that trans people aren't suffering from a delusion, it's just not the same as encouraging self-harm or affirming someone's belief that they are a unicorn. Most transgender children do grow out of gender dysphoria, you're right about that. But trans people who have persistent gender dysphoria after puberty are most definitely not going to be growing out of it. The only best treatment option for the majority of trans people is social and medical transition. It significantly improves their lives. We've been told that transition isn't going to be a miracle cure and solve all of our problems, and the majority of therapists tell that to us outright. However, the good outweighs the bad. Forcing a trans person to just "accept" their bodies when they clearly show signs of permanent gender dysphoria is the same as conversion therapy. But it really should be a last resort to transition, because it is a difficult path and it's important to be making the right decisions.