I mean, that'd be an unpopular opinion because it's pretty much literal torture for someone with gender dysphoria, yeah. It also makes the process of transitioning notably more miserable, for little to no gain. Folks can be pretty damn sure of some things well before they're 18, puberty or not.
To put this in a way that you might here Conservatives speak: "How can a person know they want to be the opposite gender, when they haven't even finished experiencing their own yet?"
The fucked up thing is I've heard that one more than once from absolute vile sacks of shit that were recommending LGBT folks be raped into cis conformity. Not metaphorically raped, either, but an explicit "you have to be this actually fucked to have experienced your gender, consent be damned" type of deal. It's not a line of thought you'd find particularly sympathetic, I don't think.