Booze, smokes, tattoos, drugs, driving, guns, and probably at least half a dozen other things I can't think of that minors aren't legally allowed to do.
Oh but get chopped up, mangled, disfigured on an operating table on a whim - no problem. Not to mention the harsh side effects of the drugs.
Even worse, parents forcing it on a boy because he played with a doll for a few minutes one afternoon.