Spiral Nebulas - Why Didn't They Carry the Day?

Astronomer Adrion von mannan found that spiral nebulas were rotating. This meant the spirals must be distant island universes as big as the milky way. But material objects can't normally move faster than the speed of light, which would mean they had to be much smaller and closer. Only a few held on to the island universe theory but others produced their own arguments for why it was wrong.