I wonder if Tolkien, when conceiving Aragorn's decree, had in mind the effect of colonisation on indiginous peoples. Perhaps he was uncomfortable with the possibility of the Shire being colonised, and its resources plundered, by the Big People. I'm not suggesting any kind of allegory here (God forbid
), but the circumstances of places like Africa and the Indian Sub-Continent may have guided his thoughts, given that many former (UK and other European) colonies were seeking, or being given, their independence at the time that he was writing LotR.