Well though-out arguments on both sides. Pieces like the "Elgin" marbles, various obelisks, portions of the temples at Angkor, etc., are perhaps the hardest to address, as the point Yannis made is a very good one - they are part of a larger context that still exists in the country of origin. The trend that I see is that these are slowly being returned to their native lands, which personally I think is good, but only if they will be protected and made accessible by the public.
It is unfair, again in my own opinion, to demonize all collectors past and present as despoilers of others' cultures. While very likely that artifacts were taken home as trophies and/or curiosities, it is also true that for whatever reason they were taken, they were in many cases saved from destruction. Another trend that I see is people around the world who had previously not given much thought to their heritage now taking great interest and pride in it. The number of anthropologists and archeologists working in their own countries is always increasing, the ideal (to me) being that the past be studied by those to whom it most directly belongs (not exclusively, mind you, but in active part). Interest and pride in their Scythian heritage is spreading among Russians, of Meso- and South-American cultures among the indios, Khmer culture among the Cambodians, etc. It is fortunate, I think, that there was enough interest by someone to preserve whatever small portions of a foreign cultural heritage until the day were it can be accepted, understood, and appreciated, by the heirs.
Sometimes good things are done for the wrong reasons. They are still good things, though.
