[mort96]

The thing is, it's an extremely simple mechanism which solves all our problems at once. Everything that's currently explained by that of one extra particle, would need separate explanations without dark matter; general relativity + dark matter fits all the data we have. It's not just about galaxy rotation speeds, it's about observations of gravitational mass (as measured by lensing) moving independently from the visible mass, it explains structure formation in the early universe, and other stuff.

It's such a simple explanation which explains so many otherwise unexplained things that I feel we should have pretty strong priors that it's true.

It does make the prediction that there's a lot of detectable massive particles out there. That's not a prediction which is easy to test, but to say there are no predictions isn't right.

[TremendousJudge]

My point is that the same could be said about phlogistons back in the day. There were a lot of completely different advances in the understanding of physics and chemistry needed to explain combustion and oxidation, and it's a lot more complex than just saying "because phlogistons". It was an extremely simple mechanism which solved all the problems at once, and fit all the data available at the time.

And it doesn't explain anything! We have this entirely new substance and we don't know what it is, what it's made of, where it came from, or why we only have circumstantial evidence for its presence.