The recovered memory bullshit was already discussed but I'm going to say eugenics. Before the Nazis' disgusting abuse of it was discovered and human rights became a hot button issue it was pretty common to sterilize low IQ or poor mothers, tards, and other undesirables without their consent. It's not black and white so it's an uncomfortable discussion because it's kind of shitty when people keep popping out fucked up tardlets that get taken right off them by the state anyway and they're just propagating suffering, but doing things like sterilizing, let's say very retarded women who love the idea of a baby but would end up hurting it out of frustration or unintentional harm/neglect and do not understand the implications of reproducing, is more nuanced. There's also the arguments about male tards being sexually aggressive, or the rampant sexual abuse of female tards in care homes, and the resultant pregnancies, they obviously can't consent to abortion or sterilization/castration but who then makes that decision for them? Is it a slippery slope to declaring anyone you damn well please with any mental health diagnosis unfit to reproduce? I don't know, but the Nazis did a hell of a job shocking everyone into seeing the worst case scenario of what it could lead to.Is there any historical precedent where a now deemed backward medical practice, once had a political movement of supporters and 'patients' advocating for it? Because if not, this transgender activism is the first time I've ever seen anything like this. While I view transitioning a very questionable treatment and it should be rather viewed as extreme cosmetic procedures than a legitimate way to treat body-image issues - it might be difficult for it to go down the bin as medical malpractice in a near future because other dubious medical practices in the past (eg. lobotomies) did not have political movement and people who would be voluntarily getting lobotomies.
Although if gender movement eventually falls apart and became obsolete like many people have stated here, I wonder how will we look back at these time? I guess no one involved in the movement will ever want to be held responsible or they would act like victims and never their fault anyway.
Also punitive psychiatry but that was more of a Russian thing. Maybe the Catholics being anti-birth control until AIDS got so bad the Pope said it's fine to wear a condom for STD protection. Actually anything the Catholic church does.