Take the Taliban example of destroying Buddhist culture in the 90s. They are/were the current people in power would you suggest returning items to be destroyed or carefully preserving them for future. Would you return items to a place incapable of taking care of them?

> These museums didn't just pop into place for the artifacts to reside in; they were built to show off their spoils.

You have a very cynical and skewed view of things. These museums were built specifically for the public good, to show off things that were of no interest in their original countries at that time. The British didn't say they wanted to build public museums to increase tourism, that came later as an unintended consequence.