Ignaz Semmelweis tried to convince the medical establishment that washing hand stop'the spread of disease in hospitals. His colleagues responded that doctors are gentlemen and gentlempdo not have dirty hands. Semmelweis was committed to a mental institution soon after and died from an infection as a result of a beoti'he received from institution workers. A few decades later the four humors school of medicine was replaced with diseases caused by microorganisms.

Not exactly a scientific debate, but among the general public there was strong opposition to the idea that rocket engines would work in space, where there’s “nothing to push against.” Famously, the New York Times editorial board mocked Robert Goddard (the rocket scientist that now has a NASA space flight center named after him) in a 1920 article:

“That Professor Goddard, with his ‘chair’ in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react — to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools.”

Image of the editorial

The New York Times eventually formally retracted that op ed, on July 17th, 1969 - while the Apollo 11 crew was already en route to the moon. The retraction is pretty funny:

Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th century and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error.

Retraction source

“‘There was some wonderful stuff about [railway trains] too in the U.S., that women's bodies were not designed to go at 50 miles an hour. Our uteruses would fly out of our bodies as they were accelerated to that speed.’” From: https://www.wsj.com/articles/BL-TEB-2814

There were (and are) a ton of utterly ridiculous beliefs about what can cause harm to women, but I find this one particularly amusing in an age where millions of women fly on planes. Imagine the plane takes off, leaving all those wayward uteri spinning in the dust at the gate…

This isn't exactly a 'science debate' but I've met several people that still think the 'Great Wall is the only man made object visible from orbit.' I read somewhere that may come from a dream some Chinese king had like 1000 years ago.

Almost crazier than flat-Earth in terms of being easily disprovable just by thinking about it for 20 seconds, but people have stated that to me as a fact and were kind of incensed when I explain it's obvious nonsense.

Personal favorite is probably Lamarckian Inheritance. Feels like super buff people having wimpy ass babies would key people in that acquired traits weren’t being passed on.

But it’s also the textbook example of how science progresses even when the underlying model being used is incorrect. Darwin credited Lamarck for suggesting a potential mechanism for evolution. Works prior to Mendel were direct tests to Lamarckism. Mendel responded to those, and on and on it goes. Lamarck helped push the field along and that’s great.

Side note, people like to say epigenetics is a continuation of Lamarckism but I’d disagree completely. Heritability of traits is what is important here, and epigenetic marks don’t necessarily tag the genes that contribute to the traits themselves.

Pretty wild to me that it took as late as it did to figure out spontaneous generation wasn't real.

The funny thing about heliocentrism is, that isn't really the modern view either. The modern view is that there are no privileged reference frames, and heliocentrism and geocentrisms are just questions of reference frame. You can construct consistent physical models from either, and for example, you'll probably use a geocentric model if you're gonna launch a satellite.

But another fun one is the so-called discovery of oxygen, which is really about what's going on with fire. Before Lavoisier, the dominant belief was that fire is the release of phlogiston. What discredited this was the discovery of materials that get heavier when burned.

Do people get sick because of germs or demons?

Continental drift or just the idea that the continents move. And it makes sense, looking at a map of the earth, you can clearly see that some landmasses look like they fit together like puzzle pieces. Combined with the fossil record with also supported this, it seems obvious to us now, the continents were once all one landmass. However, back then, the issue was Alfred Wegener, who came up with continental drift, didn't have an adequate mechanism for how it worked. The question on everyone's mind was, if the continents moved, HOW did they move? There wasn't a good answer. It was suggested at one point that the continents maybe just plowed through the ocean crust. But that idea doesn't work because the ocean crust is too rigid. So without any mechanism to get it to work, many geologists simply dismissed the idea. And to be fair to them, most of what Wegener claimed was indeed wrong.

Further advancements in geology and technology allowed for a better understanding of the earth. A key finding was paleomagnetic stripes on the ocean floor which proved that the earth's crust, and the continents must be moving. This, combined with other evidence helped construct the modern theory of plate tectonics.

People (=male doctors) postulated that when women are emotional or horny, that's a sickness called "Female Hysteria".
It was caused by the womb wondering around inside the body.
The cure was to trigger "Hysterical Paroxysm" by a doctor stimulating her genitals with a vibrator.