And they should continue changing by repatriating artifacts if the original owners want them back. It's entirely possible that some cultures might prefer having their artifacts be kept by others, but that clearly isn't always the case. For instance, bones and sacred items taken from indigenous peoples.

And as far as instability is concerned, a lot of that was caused by the same imperialist governments that looted the artifacts to begin with, so blaming those governments for that doesn't seem fair.