I think dark matter (and dark energy, for the same reason) invite lots of armchair discussion by curious non-experts precisely because they are basically fudge

I think dark matter (and dark energy, for the same reason) invite lots of armchair discussion by curious non-experts precisely because they are basically fudge factors. There's no ontological baggage and the theories are fairly "decoupled" from other aspects of physics. It's basically data, a fitted curve, and some X factor (or Lambda for dark energy) added on to make the data fit the curve. That X does not interact with any other models outside of cosmology in any currently observable way, and not for lack of searching. That makes it really tempting to think "well maybe it's the model/equation that's wrong", which has been exactly the case throughout scientific history: planet Vulkan vs Relativity, phlogiston vs oxygen, luminiferous ether vs QED.