This is only a problem for those who still want to insist that such structures (spiral galaxies in this case) are held together by gravity, the weakest of the basic forces.
“This is only a problem for those who still want to insist that such structures (spiral galaxies in this case) are held together by gravity, the weakest of the basic forces.”
Just because gravity is “weak” doesn’t mean it has no effect. Take this as an example: humans can jump and totally overcome earth’s gravitational pull (albeit temporarily). Whereas, Moon (which is much bigger) keeps on orbiting earth. Moon cannot even temporarily escape Earth’s gravity.