There are multiple observations on many different scales (all of them large) that point toward the existence of dark matter. The remaining work is to identify a particle or particles that make up dark matter. Other than that, it should be no more mysterious than neutrons. You do believe in those don't you?
I understand the argument for dark matter and dark energy. It is the hypocrisy of the evolutionists on this subject that amazes me:
"Science" believes in dark matter and energy not because they can detect either one but only because they can "see its effects." IOW, Something is happening for which there is no current reasonable explanation. Therefore dark stuff. Here's the hypocrisy: They can see the effects and realize there must be a cause, but when it comes to the origin of the universe, a First Cause is denied.
Similarly, as with the existence of God, we can see the effects of a Designer, but refuse to acknowlege Him even though the alternate explanation, chance, is absurd.