The labeling of things in museums as "stolen" is lacking, IMO. In some cases, yes... straight up looted items are in museums. In other cases, though, the items could easily have ended up lost to time (or political, economic, social turmoil) if they had not been taken and put in museums outside of the places where they originated. Additionally some of these places would not have had the means to care for antiquities b…
This is a bad argument, because it's irrelevant.
Imagine getting your car stolen, and the thief says it's justified because he is rich (partly due to stealing a lot of cars) and he can afford to send the car to the shop for maintenance more often.
The object belongs to the original owner. Even if that original owner would choose to destroy or damage their object on purpose that would be up to them.