To me its tragic that the smartest human to exist in living memory had his societal, socialist worldview swept under the rug by the capitalist pigs. We acknowledge he laid the groundwork for our understanding of physical reality itself, but sure lets pretend he didn't know what he was talking about with regard to improving our relatively simple by comparison exploitative inter-monkey social systems.

https://en.m.wikipedia.org/wiki/Political_views_of_Albert_Einstein

Einstein disagreed with probabilistic quantum field theory, which is a teachable moment that we all have limits to our capacity to understand.

Dark matter is a factor in multiple scientific models, which in turn are simulations of reality. We only know so much about the real and have to take guesses (often very accurate guesses we routinely risk our lives on). Some of cosmological guesses involve mass with no detectable signatures, id est dark matter.

What is dark matter? We don't yet know. Can something else be otherwise throwing our numbers so that it seems like there's dark matter? Sure.

That's not insanity, but an unknown, dark matter may yet reveal itself (become less dark) or it may go the way of aether and phlogiston.