You make a very well reasoned point, and I don't disagree with you. I can see why museum curators won't release antiquities because in your examples establishing provenance and actual logistics would be a nightmare. Not to mention the precedent of giving away some country's items but not others. But, at this point in time it's also a point of contention, rightfully so, that items obtained are still viewed as the property of the British museum in what amounts to a trophy case of imperialism. Ultimately we are in a period of growing pains as society and this is just another awkward period we have to get through to move forward.