***Should we believe that hordes of boogey men exist? Dark matter equals boogey men. Occam's razor applies here.***
Let me bounce this off of you and get your reaction. Occam's razor applies in situations where we are multiplying entities more than it is required based on the known inferences to the best explanation (IBE). That being the case, we have some justification based on the success of Einstein's gravitational theory to infer undetectable matter. Particle physics has already shown that some massive particles do not strongly interact with photons. This matter is difficult to detect by electromagnetic detectors (e.g., radiotelescopes and telescopes), so it isn't unreasonable to suggest that 90% of the matter in the universe has a weak interaction with the photon.
Carrying that further, it seems to me that string theories, a collection of our more promising developments in recent physics, has been alluding to the existence of massive supersymmetric particles. It may prove to be false, but I don't think this is contrary to Occam's razor to rule out such theories and hypotheses just on the basis that these are 'boogeyman' hypotheses. If that were the case, Dirac's prediction of the positron (anti-matter) should have been seen in the same way. For that matter, much of the history of particle physics would be included in that category since many of the particles were predicted prior to their discovery (e.g., W, Z, quark, etc).
Warm regards, Harv