Many of those folks who want to deny hormones/surgery to trans folks have no problem with an eighteen-year-old ciswoman getting married and having a kid. And that involves a permanent change to her body, and could endanger her physical health, and is a decision she may come to regret, *and* has repercussions for people besides herself.

Adults get to make decisions about their bodies. Adults are able to look at the options and decide whether something's worth the risk. Adults do not need to be protected from regret; the potential of regret is part of the freedom to choose what one does.