I think you're getting confused by the other circular arguments in the thread. Nobody is arguing that some guy's private collection is a museum. The discussion was about the fact that a museum doesn't necessarily allow public or scholarly access to all of its holdings or collections nor will most museums allow duplication of materials under copyright. It just shows the absurdity of claiming that this is all about the need for preservation when the reality is that a lot of people in this thread really only care about public access, even if that means utilizing methods that are morally or ethically wrong to obtain that access.
No, that's exactly what started us down this idiotic "museum" discussion path. Someone compared the collecturd in question's private stash of secret squirrel arcade porn to a museum, and then everyone went off on a tangent about what kind of behavior constitutes a museum or not.
Every decent Museum has a gift shop where every single member of the public has the opportunity to obtain a duplication of their displayed works.
No, there aren't museums that are hording vast collections not on display. They may occasionally hold certain items in the non public areas for the purpose of preservation, or due to space restrictions or display rotation, but no publicly accessible museums are hiding vast collections in reserve, in perpetuity. That's simply not true. It's a strawman you've invented to justify your argument.
Morals and Ethics are wholly subjective arguments. IT can just as easily be argued that withholding these items from public view is morally and ethically damaging.