[sarbaz]

The counterargument given by one of the proponents of MOND (a non-dark-matter counterargument) is that the bullet cluster can be explained by a combination of slight modification of GR, and additionally by the presence of a significant (but not crazy) amount of cold regular matter. Cold regular matter can't be easily detected because it isn't emitting any light, but it is just regular matter.

I'm not actually familiar with the specifics so I don't know whether this is actually a good explanation, but it's at least worth discussing.