Has there ever been anything originally dismissed as pseudoscience that was later proven to be legit?
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?
A lot of mathematicians made fun of imaginary numbers when they were first proposed. In fact, the name "imaginary numbers" was actually given by skeptics to make fun of it. It kinda makes sense, imaginary numbers are all based off of a couple fairly strange assumptions, but they make otherwise difficult problems solvable.
The whole thing kinda ruined math though. Nowadays, mathematicians spend their entire careers building frameworks based on silly assumptions in the hopes that one day it'll be useful.
Reminds me of the Big Bang Theory, which was named that as a joke. The story goes that a Catholic Priest pitched the idea and scientists basically laughed, labeling it a "uniquely catholic idea that is more scripture than reality"
Then they proceeded to look into something called "Steady State Universe" to show that Priest how silly his "Big Bang" was...
Apologies were owed when Big Bang turned out to be true, Einstein had himself photographed with the guy even.
Which is why I find it funny that today the Big Bang Theory is not only used as proof against God's existence by secular communities, but is fiercely objected too by fundamentalist ones.
People had similar responses to the ideas of negative numbers and irrational numbers when they were identified. There's a story that a follower of Pythagoras was drown for identifying irrational numbers. I suspect it's not true, but certainly it seems people had a hard time grasping the concept.