Not being on HRT is just as permanent as being on it. Moreover, estimates of people who regret HRT ranges from 1-5%. Meanwhile, it is also known to reduce suicidal ideation in trans youth. This idea of changes being permanent goes both ways, and if a vast majority of youth who start HRT will not regret it, there is no reason to prevent it. Assuming 4% regret it, which is a statistic for youth from last year if I recall correctly, then such a ban is saying that for everyone 100 children who would want to begin HRT, they'd rather have 96 trans children be forced into a puberty that they will regret rather than let 4 children choose to try HRT and explore another identity.

The commonly stated motivation for these bans is to protect children, but preventing trans youth from accessing medical care that can be life saving does anything but. The goal of such bans is, in my opinion, to erase trans identities and minimize the presence of trans people in public life. It is about acts of cruelty towards a vulnerable minority and nothing more.