As far as doing what they like — people who ride motorcycles without helmets end up costing society a great deal in medical expenses, and so where I live there is now a helmet law, despite fierce objections from riders who want to do with their bodies as they like.
We have NO idea what the long term effects of a lifetime on cross-sex hormones will be, but those costs will be borne by society, not by the individual who wants to do with their bodies as they like. This is true even in the US’s crazy healthcare system.
We can’t police smoking, drinking, and all sorts of other behaviours that create society-wide economic health expense risk, and I’m not at all advocating that we should.
But in gender clinics, doctors are actually inflicting disease state onto healthy bodies. The female body is not meant for male levels of testosterone — this created a disease state in Buck Angel that nearly killed Buck.
(Though perhaps oestrogen is actually healthy for males, since it’s protective against heart disease and also anti-depressant in males — who knows? It wouldn’t surprise my built-in irony metre one bit if gender medicine ended up being beneficial to male bodies and injurious to female bodies.)
Inflicting disease state is something doctors do to, say, cure cancer. But there is NO organic disease doctors are combatting when they inflict disease in gender clinics.