If the Universe follows Einstein's General Relativity as its law of gravity and the Big Bang picture of the Universe works is how the Universe works, then the laws of physics say we have to have dark matter, writes Ethan Siegel.

All he was General Relativity + the Big Bang and the rest he figured out from the physics: by computing predictions and comparing them with the data.
You want a Universe without dark matter, and -- at the very least -- you have to throw out General Relativity.