The British Museum has vast collection of Parthenon sculptures from the Acropolis of Greece. These marbles are sometimes called the 'Elgin Marbles', after Lord Elgin who brought these marble pieces to Great Britain in the 19th century.
In the modern days, the Greek Government is requesting the British Government to return all these sculptures as they are considered "stolen" artifacts from Greece. The British Government however denied the claim.
The judgement on morality is somewhat contemporary to the time people live in. Something that was right in the last century maybe wrong in the eyes of today's people.
However, something that has been "taken" from the other people should be returned if it is not acquired legally. I do believe that some of these sculptures were plundered.
Even then, the British Museum still refuses to return any sculpture to the Greek Government. Well, it is not for me to do any judgement, so let's just admire the sculptures while they are still in the British Museum. Nobody knows where they are gonna be in the next 100 years.