I don't see any reason to think that Tolkien discounted property rights in general, as you suggest.  He was certainly very protective of his own copyright in LOTR, including writing a forward encouraging people NOT to by unauthorized copies.  In the Scouring of the Shire, Tolkien shows contempt for the confiscation of food and leaf by the Chief's hobbits.  For Tolkien, theft is clearly wrong, which is an acknowledgement that the vitcim of the theft had a valid claim to the stolen property.  I submit that Bilbo did not feel comfortable keeping the troll hoard because it was stolen property, not because Bilbo felt any qualms about owning property in general.

The Silmarils are a different story, because the light of the Trees (as opposed to a piece of land) is not something one should seek to possess exclusively.  But note that the Valar implicitly acknowledge Feanor's exclusive rights by asking him to give up the Silmarils voluntarily, and Aule emphasizes the significance of the sacrifice for which the Valar are asking.  Would it not also have been wrong for the Valar to take the Silmarils from Feanor against his will?  I think this episode very much supports Penthe's thesis.  Property ownsership conveys rights, but it also conveys responsibilities to contribute to and maintain a just social structure.  Hoarding means enforcing the rights but failing to recognize the responsibilities.

I think Penthe's approach also helps make sense of the last few chapters of The Hobbit.