With enough time and medical advancements, most medical practices of today will look bad in retrospect. There's a chance that one day, we can find the root cause behind gender disphoria and can help people suffering from it to feel at home in the bodies they were born with, if they want to. But at the moment, gender reassignment surgery is for many patients the best treatment on offer, with a "regret" rate that is far below what some people want to make you believe and a marked decrease in self-harm and suicide incidents.
I can see that there is an argument to be had regarding the treatment of children, but for adults, the outcome is generally positive. And in the end, it's their body to do with as they want to.