"It is better to remain where it is seen by millions than be returned to its country of origin".
Basically, though, this is the bad side of colonialism.
One such questionable "acquisition" is the huge collection of things in the Pergamon Museum in Berlin, Germany. Yes, by visiting these in Berlin, it is far more likely I would see them than had they remained in the Middle East. At the same time looting is totally wrong.
In the UK we are under pressure to return the "Elgin Marbles" to Greece. Personally, I think we should make exact copies and return the originals to Greece.