The suggestion that OHV riders are responsible for vandalizing "Open" route markers doesn't make much sense. Why would an OHV rider do what is decidedly not in his best interest? If he vandalizes the "Open" markers, all he succeeds in doing is reducing his available trails. Why would he do that?
On the other hand, someone who seeks to close all trails would have everything to gain from vandalizing the "Open" route markers. He confuses those OHV users not already familiar with which trails are open, and increases illegal riding too close to homes, which in turn leads to increased resistance to ANY open trails in the area. Taken to your logical conclusion, where illegal riding begets closures, this approach would result in fewer open trails, not more of them. The vandalism can then be pinned on the OHV rider as a further "reason" for closure and public outcry against all OHV use on Limited trails.
Non-compliance is YOUR friend, not mine.