It's perfectly sensible to say "You can't take it with you" and ask your relatives to sell your clothes and keep the casket closed--as long as that's your decision. It is not OK to impose that same unattachment to material things on someone else, especially when there's very little they can say about the matter. If Deadman Joe wanted to be buried with his boots on, then removing them, even after he has no earthly use for them anymore, is denying him his eternal rest. Why do you think Revenants are so grumpy all the time?
I'm of the opinion that taking things from graves is all right provided it's done for reasons other than personal gain: Samia's purported intent of historical research on King Strohm III, for instance, or the aforementioned borrowing of the gear of some historic warrior to defeat some danger that threatens the land (and then putting the gear back), or for study. Storing relics in a museum, though, is of dubious morality if their original owner would miss them--making facsimiles and putting the actual relics back where they came from is the best bet. I also believe that if the person has been dead for so long that nobody even remembers who was entombed there, their attachment to this earth has faded so much that their former possessions are pretty much up for grabs.
Now that I look back on that last sentence, I just justified the almost comlete lack of Virtue hits for looting the Graveyard District, since the only tomb with a name on it is Jeeves's. So I'm going to have to clarify my ideals through the lens of BG, and say that taking stuff from people like Kangaxx, the Crypt King, and Bob the Lich (in the Crooked Crane) is all good, but there's really no way to feel morally righteous about nabbing the Staff of Curing.