We have a very good theory of gravity, general relativity, and actually for anything that was ever used to build anything including the Voyager probes, Newtonian gravity is enough. In a sense we even have a safety net.

As for dark matter, the reason we don't have a good idea what dark matter is, is that is has almost no effect on normal matter. So the reason why we can ignore dark matter everywhere except at the frontiers of physics is, that dark matter only matters when one spends awesome resources to try to detect it.

Dark matter isn't "ignored", it is unknown. Not because nobody cares but because, as the parent said, the current scientific paradigm is incomplete and by extension incorrect.

Well then, we'd have a comprehensive idea of sociology, too, on account of society not completely collapsing.