Why don´t you explain HOW and WHY *dark matter* showed up in the scientific minds at the first place, before you´re continuing the dark speculations with all kinds of *small nothings*?
I thought I just did.
A discrepancy between observations and theory was found. There are *two* ways to proceed from this:
1. Either say we missed something OR
2. Change the basic theory.
In ALMOST EVERY case, the reason theory and observation differ is because of 1: we missed something.
In the case of stellar motions in galaxies, there was a LONG history of discrepancies being due to some extra mass existing that had not been known before: that is how Neptune was discovered.
So, to postulate some extra mass that was not previously known was completely appropriate and in line with historical successes.
As particle physics progressed, examples were found that do NOT interact with light: they are dark. ONE example is that of neutrinos. So the possibility of extra mass being a result of some new subatomic particle was quite reasonable and something to be investigated.
Furthermore, the hypothesis of extra, unseen mass, had OTHER consequences that were subsequently observed. This is confirmation of the original hypothesis. Also, other possibilities for this 'missing mass', such as white dwarfs, small black holes, etc, were eliminated by *actual observations*. This increased the possibility that a new subatomic particle was involved, which made the problem much more interesting.
Also, alternative explanations (change the theory) were considered: MOND, for example, had some success in producing results that agree with observations, but it has some very ad hoc aspects to it. When the Bullet cluster data came out, MOND was found to *also* require some missing mass. So in *either* case, some sort of missing mass was there.
This is how science works: we find some hypotheses that agree with observations and use those to propose new observations as tests. Those hypotheses that pass such tests gain in stature. Those that don't lose stature.
In the case of dark matter, the differences between observation and theory lead to a *hypothesis* of extra matter. That hypothesis was made more reasonable by aspects of particle physics and was also supported by other types of observation. We still do not know *which* subatomic particle is responsible for this extra mass. ONE possibility that was considered were neutrinos: there are a LOT of them, they are 'dark' (don't interact with light), and have some other properties associated with dark matter. It turns out that neutrinos were excluded because of the effects on galaxy formation.
But, the basic idea that there is extra mass that we cannot see is completely appropriate given the history and connection to other areas of physics. It is also in agreement with a range of observations.
To compare, your favorite theory, EU makes NO predictions of new observations. It has NO way to explain even the motion of planets in our solar system. It has no details on how to explain the motions of stars, and it is frankly contradicted by numerous observations.