So dark matter doesn't just mean "not illuminated" it means it doesn't interact with the EM field at all. However it does interact gravitationally, and this has

So dark matter doesn't just mean "not illuminated" it means it doesn't interact with the EM field at all. However it does interact gravitationally, and this has a measurable impact on matter we can see with our telescopes, the cosmic microwave background, etc. Cosmology today is, in general, very sophisticated. I mean no offense but armchair contrarian takes here are very much just coming from a place of ignorance. Any criticism we can imagine as lay people has already been plumbed to a depth and detail we will never be capable of in our lives. One can point out that there's always some degree of uncertainty in absolute terms, but I think the appropriate understanding is Bayesian, and I'd sooner bet on getting hit in the head by an astroid walking through my neighborhood than that cosmologists have this all fundamentally wrong. The wikipedia page does a reasonably good job of going through the multiple independent lines of evidence we have for dark matter. Sean Carrol has some great posts / videos in this topic area as well. The reason we're so confident of the current state of knowledge is not somehow that physicists and cosmologists suffer from hubris that blinds them to sophomoric criticisms, though sadly there's a number of people who continue to grind that grift.