I have seen some papers claiming that Einstein said there is no Black Hole in the real world, here is a phrase from Einstein himself, see this arXiv preprint:

The basic result of study is the distinct understanding that there are no Schwarzschild singularities in the real world. Thought the offered theory considers only such systems, in which particles move by circle trajectories, we have to hardly doubt that the investigation of generic case will lead to the same results. The Schwarzschild singularity is absent, because the matter cannot concentrated in an arbitrary way;otherwise particles composing the clump will reach the speed of light.

Why did Einstein say the particles composing the clump will reach the speed of light? And why haven't other physicists accepted his argument?