Your paragraph 3 is the basic theory around medical gatekeeping: in many societies, children just plain aren't
powerful enough to be in a position to give informed consent, unless special measures are taken to rule out undue influence. (In this case, that'd be: a diagnosis of gender dysphoria, which involves a psychologist asking you awkward questions for a few hours; and then ensuring all subsequent consent is informed, and in accordance with the psychologist's findings.) That's also why we have the "compromise" of puberty blockers (safe, reversible), but not any
permanent treatment until the child reaches Gillick competence (in Norway, age 16).
The trouble I have with this reasoning, though, is it's asymmetrical. We don't allow trans kids access to exogenous sex hormones because cis kids might hypothetically be being influenced by their parents / other authority figures to make a bad decision (e.g. Munchausen syndrome by proxy), but we know there's pressure on trans kids to repress and pretend to be cis (we have statistics about it), so why do we let any children go through puberty? How can we trust them with that? (Yes, this thought experiment is somewhat ludicrous, but why is it ludicrous?)
For most people who experience it, gender dysphoria is distressing and hard to ignore. Most cis people can be put in situations where they experience it, and they report the same intense feelings of distress. I doubt you could easily influence many 12-year-olds to push through those feelings – though I'm not sure how one might test this ethically, so I'm not sure what studies to look for. Norway's current approach seems suitably-conservative to me. (And I don't see any advantage, even hypothetically, to forcing trans people into binary classifications: that seems like the "rigid gender roles" problem rearing its head again.)
P.S.: You're considerably more reasonable about this than I initially thought: thinking about the right things, for the right reasons, such that with complete information I'd expect you to come to the right decisions. I long to have people like that for political opponents.
The trouble I have with this reasoning, though, is it's asymmetrical. We don't allow trans kids access to exogenous sex hormones because cis kids might hypothetically be being influenced by their parents / other authority figures to make a bad decision (e.g. Munchausen syndrome by proxy), but we know there's pressure on trans kids to repress and pretend to be cis (we have statistics about it), so why do we let any children go through puberty? How can we trust them with that? (Yes, this thought experiment is somewhat ludicrous, but why is it ludicrous?)
For most people who experience it, gender dysphoria is distressing and hard to ignore. Most cis people can be put in situations where they experience it, and they report the same intense feelings of distress. I doubt you could easily influence many 12-year-olds to push through those feelings – though I'm not sure how one might test this ethically, so I'm not sure what studies to look for. Norway's current approach seems suitably-conservative to me. (And I don't see any advantage, even hypothetically, to forcing trans people into binary classifications: that seems like the "rigid gender roles" problem rearing its head again.)
P.S.: You're considerably more reasonable about this than I initially thought: thinking about the right things, for the right reasons, such that with complete information I'd expect you to come to the right decisions. I long to have people like that for political opponents.