At the moment of writing this, there is no alternative theory that can adequately explain the behaviour of cosmological structures better than dark matter.
There is no one dark matter theory.
There are about a dozen dark matter conjectures, each giving dark matter extraordinary and unproven attributes.
And none of these conjectures explain the large scale behavior of galaxies, while being consistent with experimental evidence collected in our neck of the woods (for example, dark matter being completely uniformly spread out, etc).
Dark matter is simply a mathematical placeholder; arguing that we even have a convincing - aka, in accord with all experimental evidence, with properly determined characteristics, etc - conjecture as to what it is says more about the arguer.