How the Edge of Our Galaxy Defies Known Physics

The rotation profile of galaxies doesn't fit visible mass and gravitation. IT DOES NOT FOLLOW THAT "it couldn't spin as fast as it does without dark matter". It is not true that "the only thing that can hold [orbiting mass] is gravity."  There are many assumptions here, especially that gravity is the sole significant force at cosmic scales. Oh, assuming that we fully know the distribution of mass of the universe (hint: we don't) and that gravity is the sole force acting on everything (it isn't) THEREFORE DARK MATTER!"

Hint: EM fields are not negligeable on cosmic scales. Gravity is, actually. Sure, electric fields and magnetic fields alone are constrained by the cube of the distance, but not all EM phenomena are affected with distance. Photons, for one, should point out how common it is, and collimated plasmas, on the other, should underline its significance as well, as this is the structure of the cosmic web. IT DOES NOT FOLLOW THAT dark matter is necessary at all, and considering how it's increasingly being disproved, did not earn/does not deserve the privilege of being used as working hypothesis.