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.

Continental drift was a theory formed in 1912 by a German meteorologist, Alfred Wegener. Geologists balked at the idea of enormous landmasses moving and said the idea of an Urkonintent was ridiculous. And besides, he was a weatherman, German weatherman, so outside of his field and untrustworthy as a German was considered at the outbreak of WW1.

Then, 50 or so years later his theory was rediscovered when different fields were trying to understand polar magnetic drift evident in iron ore formation. The only explanation that made sense from the evidence is that mountains were not permanent and oceans didn't exist in some areas - a lot like the land masses moved.

Wegener was eventually vindicated in almost all areas except drift speed. There was an Urkonintent, which has been named Pangaea. The continents do move but because they sit upon plates. He had taught the world about the world but died before anyone thought he was right.

The germ theory of disease was originally very unpopular with doctors who subscribed to the miasma theory of disease. The idea that a doctor should was their hands before tending to a patient was seen as insulting. Doctors were gentlemen! Their personal hygiene was beyond reproach!

The Dead Internet conspiracy theory was written with total crackpot paranoid thinking about ruling elites, likely antisemitic undertones, and general tinfoil hat reasoning about AI. Plus generative language models were nowhere near advanced or skilled enough at the time the conspiracy was purported to be happening.

But it was accidentally prophetic in at least two ways by 2024:

1. Corporations have completely strangled online social spaces to the point that most people only visit about 1 to 3 of them, and
2. Online discourse in those social spaces has been absolutely captured and manipulated by multiple governments trying to manipulate other countries and stir them into pointless ragebait frenzies.

It wasn't due to the illuminati, the Jews, or anything weird and bigoted conspiracies of old have traditionally blamed. It was thanks to billionaires, corporate and government espionage, AI grifters, and unregulated scammer networks (digital currency counts too) jumping onto the same technology at the same time and ruining everything on the Internet in similar ways.

The fact that people with Myalgic Encephalomyelitis originally and demeaningly called Chronic Fatigue Syndrome can’t exercise.

It was first believed to be a mental health disorder where people are scared of doing activity. And patients who said exercising made them worse were treated for hysteria and kinesophobia (fear of exercise).

Now after a decade of so of biomedical research, and after research showing Graded Exercise therapy worked was discredited, we have a dozen or so 2-day CPET studies, we have definitive proof that while healthy controls improve exertional capacity by exercising, these patients are the exact opposite, they worsen.

There’s even been a couple cases of young people 20-30 having a degenerative disease state that killed them.

Bacteria being the cause of ulcers.

https://en.wikipedia.org/wiki/Timeline_of_peptic_ulcer_disease_and_Helicobacter_pylori

Quantum Mechanics: The early concepts of quantum mechanics, such as quantized energy levels and wave-particle duality, were initially met with resistance, even by scientists like Albert Einstein, who helped develop them.

Reason for Rejection: The ideas were counterintuitive and challenged classical physics' deterministic view, introducing probabilistic interpretations of nature.

Adoption: The overwhelming experimental evidence, such as the photoelectric effect, blackbody radiation, and the behavior of atoms and subatomic particles, eventually led to the acceptance of quantum mechanics as a fundamental framework in physics.

Sugar is the reason for the rise of heart disease that was happening in US. John Yudkin was the one to purpose that sugar was dangerous for our bodies and heart plus responsible for obesity but he couldn't prove it and was criticized by his scientist who were paid by the sugar industry. I forget to state the sugar industry was funding scientist to blame it all on fat. It was a pseudoscience till the 70s and 80s when they found the correlation that Yudkin was missing.

A lot of science around trees and forest management has gone this way. Forest used to be seen as competitive areas that needed to be thoroughly managed to be healthy. Now we know that’s not true at all, and overall would be better off if we just let them be (in most, though not all cases). Same with the idea that trees communicate with each other and share resources. This was dismissed and ridiculed for a long time, but has now been pretty resoundingly proven true. Peter Wohlleben’s The Secret Life of Trees talks a lot about this.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) was originally dismissed by a lot of community doctors as well as more academic medical people. There are still a few who don’t believe in it and dismiss it as a behavioural or attitude problem. Thankfully those people are in the minority now. Unfortunately that doesn’t mean they’re not in influential positions.

One surprising contributor to validating ME/CFS is long covid, which seems to be the same condition but catalysed by a different virus.

I’m not a medical expert and could have mistakes in the above post but it’s generally correct.

You've led me to quite a Christian Scientist rabbit hole, but I cannot for the life of me find the requirement to start smoking. Rereading, is that maybe a typo that should've said they required people to stop smoking? I can't find that either, but it seems to make more sense to me.

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.

Wearing masks to not catch diseases when treating patients.

Many scientific hypotheses started out as what seemed like crazy ideas at the time. When Galileo and Newton challenged the ideas of Aristotle, this was seen as fringe and radical. When Einstein challenged the accepted Newtonian dogma it was seen as scientific heresy at first. These ideas only seem mainstream to us with hindsight.

Lamarckian Theory was criticised for a long time but now we know it isn't entirely false, epigenetic changes that occur can actually be passed on.

There was a study this year suggesting Frenchmen feel pain

I think an interesting one (that is still controversial) is that megakaryocytes(MKs) in the lung actually produce a significant amount of the platelets in your body. Rather than platelets all coming from bone marrow MKs. It is interesting because these two different platelet origins have different responses to infection.

This does seem to happen in medicine and nutrition, things that start on the fringe sometimes move to the mainstream. I thought my lunatic ex was out of his mind when he said fasting could heal disease, but it turns out it can, just not in the universal magical way he thought.

Epigenetics vindicates a small portion of the theory behind Lamarckism, though there’s still a lot of research to be done to understand the actual mechanisms underlying it

The idea that rocks sometimes fall from the sky.

"Fringe" ideas are discovered to be fact a lot of the time. Nearly everything that is known to the true in the modern world started out as "some quack theory".

The difference is in how those that think of the "quack theory" go about investigating their theory and respond to the results of that investigation. And whether someone responds honestly or not to that has a lot more to do with them as a person than it does what field of study they come from.