Theories don't explain everything, and that's OK

From the Starts with a Bang blog:

Every scientific theory has its limits. It never means that the theory is entirely wrong, but pushing up against those limits often gives you clues towards either extending your theory (such as adding inflation to the Big Bang) or overthrowing your theory (such as replacing Newton's gravity with Einstein's General Relativity). In either case, the old theory is still a good theory over its range of validity, and if you overthrow your old theory, your new theory must explain all of the observations of the old theory.

Why do I bring all of this up now? Because Dark Matter -- an extraordinarily important part of modern cosmology (which you can learn about here, here, here, here, and here) -- is under attack by people who don't understand this concept.

In a nutshell, the "dark matter problem" is that on large scales (galaxies, clusters of galaxies, and even larger structures), the amount of normal matter that's present -- stuff from stars, gas, planets, and dust -- is insufficient to explain the gravity caused by these structures. The speeds of the galaxies in the image above? They're too fast, unless there's some extra unseen mass. The bent arcs of light, caused by gravitational lensing? Also require more unseen mass, but coincidentally, the same amount that the speeds require.

What about the large-scale structure that forms in the Universe?

It also requires dark matter, or gravity wouldn't work correctly. But there's something extra, that constitutes insurmountable evidence for the existence of dark matter. We've caught galaxy clusters in the act of colliding! According to the theory of dark matter, the gas should "splat" in the middle of the collision, but the dark matter from each cluster should pass right through, unaffected by the collision. When we map out the effects of gravity, if dark matter is correct, it shouldn't line up with where the gas is. Let's take a look at these colliding clusters, known as the Bullet Cluster. And let's put the hot X-ray emitting gas (from the "splat") in pink, and the map of gravitational force (as measured from lensing) in blue.

The fact that these don't line up is a smoking gun for dark matter. So if you want an alternative for dark matter, that alternative needs to explain all of these observations. And none of the theories -- not MOND, MOG, TeVeS, or any others -- can do so.
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Dark matter doesn't do everything. Its predictions on small scales are uncertain, primarily because we don't know what makes it up, and we don't know what its properties are! If we knew these things, we could make predictions. But saying that, "since the naive predictions we can make are inadequate, the entire idea of dark matter needs to be thrown out" is absurd.

This isn't a house of cards, where if you find one defect, the whole thing will collapse. It's a stepladder that's missing a rung or two. It still works. In fact, it totally works! Its flaw is that it doesn't serve your needs for every single possible class of applications. (At least, not yet.)

So yes, my theory doesn't do everything. And that's okay. It means it's just like every other scientific theory that's out there. Which is to say, it makes it possible to figure things out.