Wouldn’t a black hole that small evaporate pretty quickly?

Here's another answer to the Fermi Paradox, that while life is normal and abundant, there are lots of random possibilities for destruction such as a primordial black hole coming by.

The apparent rarity of intelligent life might be a statistical matter of there being lots of opportunities for such life to arise, but also lots of hazards of random destruction.

... on reflection, while this might be intellectually satisfying, it's not particularly nice to contemplate.

Probably not. Accretion disks are temporary, they only exist for a few thousands/millions of years after a capture event. Something has to get really close, and the smaller your object is, the more unlikely it is for something to come close enough to be consumed.

Plus the rate at which a black hole can consume mass is proportional to mass/radius. If it's too small, it can only consume matter very slowly, which means the accretion disk would be cold and quiet.

Dark matter is an observed discrepancy between measurements. There appears to be a lot of unaccounted-for mass, based on many experimental results. There are several theories as to what that observed discrepancy could be caused by. This is a well-covered topic, anywhere you could hope to learn about astrophysics. What it may sound like to you is not what it is.

I'd recommend watching a video from PBS Spacetime if you want to learn about it. They have several.

Galaxies don't behave how they should with our understanding of gravitational mechanics. The only thing that fixes the model is the addition of a lot of mass that we can't see.

That would be easy enough to explain away as an incomplete model, except we have observed galaxies which do fit our models. The only way to explain that is if those galaxies are missing this invisible mass. There's no other way to reconcile these observations.

How would you square these observations? Under our models of gravity, most galaxies behave as though they contain much more mass than what we observe. However, some behave exactly as Newton would predict. The misbehaving galaxies can be made to fit the model by adding mass in very particular locations, mainly as a halo or shell around the outside.

We can show how much mass and where it must be to make galaxies behave as expected. These calculations are the same for most galaxies with dark matter, and galaxies without dark matter require no correction. At this point we have two explanations: either gravity behaves radically differently in different places in the universe, or there's a new type of massive particle that we haven't discovered.

We know already that the standard model of particle physics is incomplete, and there are more particles to be discovered. We are also very confident that the laws of physics are the same throughout space and time, and we are very confident that our models of gravity are correct on large scales.

The simplest explanation that fits all available data is dark matter. Positing that there's a new type of massive particle that we haven't discovered isn't really a shocking revelation.

There are a bunch of good reasons to believe there really is matter there that we can't detect aside from its gravity. Here's a talk: <https://www.youtube.com/watch?v=h8KV9Ht5o_M>.

Yeah. What if space/time is just noisy?!?