The Acropolis Museum gets 1.4 million visitors a year and a ticket costs $10 to $20 depending on season. The British Museum is free and gets 4 million visitors per year.
Thus if the aim of any museum is to provide access to the most and widest range of people, rich or poor, the sculptures are seen and appreciated by many many more people and for free if they remain in Britain than if they were taken back to where they were removed.
A counter-contrarian and tech optimist take would be that digital museums technology, high-res photos, VR, video etc would vastly increase the outreach of any object in any museum anywhere in the world. So the actual objects could never see the light of day again, be replaced by high quality reproductions and still more people will see it. One might even say it doesn't matter where they are or if a museum has it, if its properly served by the internet!