It represents a discrepancy between our models and observations of the universe, which imply there is a lot of unaccounted-for non-interactive mass out there.
Dark matter generally is less a theory and more a question: Where is all this mass? Does it really exist? What can explain it? What is missing from or wrong with our understanding of physics that explains our observations?
If you want to complain about a specific theory of dark matter like lambda-CDM or challenge our understanding of gravity or whatever, it'd be more correct to name the actual theory.
Dark matter generally is less a theory and more a question: Where is all this mass? Does it really exist? What can explain it? What is missing from or wrong with our understanding of physics that explains our observations?
If you want to complain about a specific theory of dark matter like lambda-CDM or challenge our understanding of gravity or whatever, it'd be more correct to name the actual theory.