That makes sense to me. If MUS bought stones off trespassers that would just reward bad behaviour with all the unintended consequences that would bring. A carrot-and-stick approach is optimal. Bring them into the fold with some sort of official status, reward compliance and encourage reporting of usurpers.
Worst would be to allow/encourage them to self-police because I think mob justice would be harsh and probably lead to escalation and violence. Tough issue to control. When people have nothing to lose, desperate acts appear reasonable. Let's just hope there's no tribalism in that area. That's one flash point no one has ever solved.
MUS Price at posting:
8.6¢ Sentiment: Buy Disclosure: Held