Turn about: how can you justify "returning" a cultural artifact to the culture that destroyed its creators?
Huh?
Let's do this again. Maybe you'll get this analogy. As you know, there was a war between the US and Britain in 1812. Amongst many actions, the Brits torched the White House. Suppose they really looted Washington and made off with the Declaration of Independence and Constitution as war booty. (Historically, that was their goal-- this scenario has them succeed).
Suppose there was a 1816 commission that decided that the acquisition of these documents was made through theft.
Suppose Britain has refused to return them - even today.
To be consistent with your position on the Elgin marbles (bear in mind that the Brits themselves in 1816 found that the marbles were acquired through theft), you would have to say: "that's ok, let the Brits have those documents. Who cares for them. They are after all, the superior culture amd they are preserving our heritage for positerity as only they know how."