The problem of rotational curves and few other effects attributed to the dark matter appears if one applies Newtonian mechanics on a galaxy or intergalactic sca

The problem of rotational curves and few other effects attributed to the dark matter appears if one applies Newtonian mechanics on a galaxy or intergalactic scales. Yet to this day there is no proof that this is a sound approximation even for small galaxies. It is just assumed that is a valid approximation without justification. And the reason for that is that accounting for General Relativity is hard even if one consider just next order approximation after Newtonian gravity. So yes, it could be that almost everybody was doing it wrong.