I think there is an important temporal element. Much of our current understanding of world history comes from Western archaeologists prancing through jungles and deserts where the relics and artifacts of ancient civilizations dangle on the brink of total obliteration from living memory. Yes, for the 18th and 19th centuries much archaeological practice could really be described as "looting" but nonetheless the whole world gained a unique and powerful understanding of human history through these archaeologists' efforts. One need only look at the Taleban's attempt to erase all physical memory of Afghanistan's non-Islamic past to see the advantages of moving archaeological finds to the West. In fact, Afghanistan is a particularly good example because Afghanistan has been a critical crossroads for several civilizations so Afghan history truly is a world history, impacting Chinese history, Indian, Iranian/Persian, Arab, Western, Greek, Roman, and the various Central Asian cultures and civs that have rumbled through Afghanistan.
I am reminded of a scene from a dream sequence episode of
The Simpsons where Milhouse and Lisa are characters in ancient Egypt, c. 1300 B.C., when the Pharoah's head of the guard - Chief Wiggum - locks them into a sealed chamber in one of the Pyramids at Giza and he shouts down to them as he closes the chamber, "Say hello to the British Museum for us!"
There is another side to this issue though, quite separate from whether Western archaeologists should be allowed access to non-Western sites - they should - and that's whether the collections of modern Western archaeological museums should be returned to the lands from which they came. THAT I believe should happen; there is no reason modern Greece, Turkey, China, Egypt, etc. etc. etc. should not possess these artifacts from their own histories. In the case of countries like modern Afghanistan I think the West should still hang onto them until such time as they stabilize enough, but with the understanding that at some future date Afghhanistan would get these artifacts back. Just think of the lucrative market that would develop if Egypt for instance was able to re-acquire all or most of the artifacts taken from it over the past centuries; there could be a traveling exhibition of Egyptology artifacts around the world, with each museum paying to be able to display these relics for a set period. Unfortunately, many Western museums have made lots of $$$ off these artifacts and will be loathe to release or return them, but it would be a significant political gesture to do so.
