You're not the first, second, or ten thousandth person to have this thought. But dark matter fits the phenomena better than any proposed modification of gravity. See the https://en.wikipedia.org/wiki/Bullet_Cluster for a textbook example.

Also, look at the Bolshoi Cosmological Simulation (https://en.wikipedia.org/wiki/Bolshoi_Cosmological_Simulatio...). Simulating the universe with the currently accepted model of dark matter successfully predicted the large scale structure of the universe. As a model for explaining observations, dark matter does hold some merit.

Modification of gravity has been found wanting. See e.g., the bullet cluster, https://en.wikipedia.org/wiki/Bullet_Cluster

One more interesting explanation I read in Hawking's Universe in a Nutshell, was that dark matter is extra gravity coming from parallel universes/extra dimension. Basically, what if gravity warps not just this plane, but other realities as well. It would explain why gravity is so weak compared to other forces.

Well from what I know, gravity was once a misunderstood component of spacetime bending, so it would be proper.

I had some longer talk with a friend that is much more into logics about the MOND theory. The problem I have with this theory is, that I don't think that the MAX function used, is classical logic. Unfortunately, I have not found a real explanation, but we came to the standpoint, that you require some more complex logic to satisfy the MAX function and for physics, I stopped believing in anything beyond classical logic.