There is a tendency for real doctors with backing from Academia or whoever's in charge of deciding how you science to just plain getting it wrong and not realizing it for a long time.
Homeopathy is a good example of this, as it appeared to get great results when it was created during the Bubonic Plague and had such staying power to the point that in the 1800's it was considered a legitimate and mainstream field of medical practice.
Now today we know Homeopathy is nonsense... Remembers New Age Healing is still a thing Okay, those of us with sense know homeopathy is garbage. With the only reason it was getting such wonderful results was because the state of medicine for a long period of time in human history was so god awful that not getting any treatment at all was actually the smarter idea. Since Homeopathy is basically just "No medicine at all", that's exactly what was happening with its success.
Incidentally this is also why the Christian Science movement (Which was neither Christian nor Science) had so many people behind it, people were genuinely living longer from it because it required people to stop smoking at a time when no one knew smoking killed you.
Anyhow. With that in mind, I want to know if there's a case where the exact opposite happened.
Where Scientists got together on a subject, said "Wow, only an idiot would believe this. This clearly does not work, can not work, and is totally impossible."
Only for someone to turn around, throw down research proving that there was no pseudo in this proposed pseudoscience with their finest "Ya know I had to do it 'em" face.
The closest I can think of is how people believed that Germ Theory, the idea that tiny invisible creatures were making us all sick, were the ramblings of a mad man. But that was more a refusal to look at evidence, not having evidence that said "No" that was replaced by better evidence that said "Disregard that, the answer is actually Yes"
Can anyone who sciences for a living instead of merely reading science articles as a hobby and understanding basically only a quarter of them at best tell me if something like that has happened?
Thank you, have a nice day.
Off the top of my head - handwashing before surgery/delivering a baby reducing patient deaths (though you mention germ theory), plate tectonics, the evolution of species, heliocentricism.
I think it's important to detail just how much the scientific community rejected the whole idea of washing your hands. Even though Semmelweis dropped his hospitals maternity mortality rate from 18% to 2%
"In 1865, the increasingly outspoken Semmelweis allegedly suffered a nervous breakdown and was committed to an asylum by his colleagues. In the asylum, he was beaten by the guards. He died 14 days later from a gangrenous wound on his right hand that may have been caused by the beating."
https://en.m.wikipedia.org/wiki/Ignaz_Semmelweis
Holy shit
"This guy washes his hands, clearly he's crazy, take him out back; if he dies it's a mercy killing."
Was actually said by someone at one point.
Gah, I was going to say plate tectonics.
Heliocentricism is a good one, the story they teach in school was that "The Pope just didn't look through Galileo's Telescope because he believed in Jesus too much!"
In reality other practioneers of the sciences simply couldn't recreate Galileo's work and thought it wasn't worth entertaining, especially since it wasn't just an idea with evidence against it at the time, but one that was politically messy thanks to the Protestant Reformation...
I really hate it when people oversimplify history, especially to paint any organization in a harsher light than it deserves. (That and if we could get more of certain crowds to realize science is more complicated than just saying "Church bad" that would help a lot...)
So the answer is "most things".