You buy a box of old documents on Ebay. It contains an original manuscript of The Fellowship of the Ring with J. R. R. Tolkien's edits and notes in the margins. Tolkien's estate demands the copy back so they can burn it. You should mail it to them because they own it, right? It's just a book, right?

No, you shouldn't. They owners shouldn't be able to destroy it for the same reason we have laws protecting monuments and historical sites. When something has historical or cultural value, the public has a right to preserve it even against the wishes of the owner.