The same concern could be aired for Pre-colombian stuff too as well as American Indian artifacts. There seems to be a point in time where archaeology takes over from respect.
Wow, you guys bring up alot of goods points to think about. I would agree that you cannot return everything and that you are right that alot of people would never get to see this stuff. But having said that I really think it does matter to some extent on how the artifacts were aquired. I mean if it is by illegal means I really think that they should be returned to the proper place.
Alot of countries, when they hear about artifacts that were obtained illegally, actually file an injunction or suit to get them back. I've heard of that from time to time. So, if you have stuff that's iffy, hide it or give it back!