One of the best arguments FOR dark matter is gravitational lensing, and without General Relativity, the lensing could not so convincingly show us gravitational fields caused by something that is "dark" to us.
I also agree that the difference between Newtononian and General Realtivity calculations don't explain away the hundred or so galaxies we see rotating too fast by an factor of 10. (Ref: Michio Kaku)
To agree with AC above, I concur that "they" (meaning physicists and cosmologists, I assume) aren't ignorant of Einsteins work. It's just blowing off steam, I think.
So, take a deep breath.
Think of what you are grateful for.
Exhale....
Better?
-FoxPaws (who is glad she doesn't live in Cardiff!)