While people like to say they "stole" things, there's no evidence they ever took something that others actually cared about or took the least interest in protecting. The Elgin marbles were just flopped around a field and no locals seemed to care at all. Some of the items were purchased directly from their owner at a price negotiated with a willing seller.
I think the British museum is proof of how scholarship and gentle care can preserve our past and create something that people love to visit and learn about.
Let's say you come to my country and buy a souvenir. Can I decide, hundreds of years later, that you must be forced to give it back?
And why do borders matter? The argument seems to be that housing an object on one side of an arbitrary political line is morally superior to putting it on display on the other side of some invisible line. Somehow someone born to the right parents is a morally superior curator compared to someone born into the wrong parents.
Do you really think they stopped caring about? Bold claim to say this applies for every culture and artifact over there.
Or is it maybe that pillaging, which destroys what's left behind, and then having no good way to take things back other than defeating the British Naval Empire makes maintaining your own history hard?