The vices tend to go together

"Kids have full 'control over their own lives', and can buy whatever drugs they like. That's choice, you know." Putting aside your likely allusion to puberty blockers and cross-sex hormone drugs, child protectionism in the realms of sex prohibition and drug prohibition tend to go together. I don't think the flavored vape panic happened so long ago to not see the comparison. And other illicit drug use is a perennial fear among parents during the adolescent years. We can oppose the criminalization of underage drug use without being strawmanned as supporters of its normalization and I don't think it's fallacious at all to think it benefits us to undermine child protectionism even in its non-sexual forms. But coming back to the trans-drugs, those occupy a different role in the child protectionism debate. The pro-transitioners see these drugs as a way to protect transkids from transphobia (because making them look more trans somehow stops them from being a target of anti-trans bullies???). As such, they represent the institutionalization of child protectionist rhetoric and every bit compatible with sexual protectionism. There is no contradiction.