On the other, to pick a random example, why does the current Egyptian state have a right to those treasures which are the results of oppression and slavery by its predecessor states? There's a whole set of assumptions about nations, national myths, rights of succession and such things that I'm not comfortable making and haven't thought through. Should the Egyptians apologise for their colonial days first? When does the statute of limitations run out on these things?
If I had to make a judgment call, yes, I'd say the modern Egyptian state has more "right" to them than the modern British state. They are Egyptian, and a part of Egypt's cultural heritage, the bad with the good. That said, they are also clearly parts of British history, at least in the obtaining of them, although they are not generally displayed as such.
I wonder... if the Beowulf manuscript were housed in the Louvre, do you think the British government would be asking for it back?