10 Year PSL owner here.
PSST. The "opposing fans" issue in Bank of America stadium? It's not because PSL Owners are selling their tickets. It's because Panthers' "fans" aren't buying them.
The choice to sell a ticket is objective. Ticketmaster is a platform without allegiances or fandom. Instead of trying to figure out how so many opposing fans got tickets, you need to start asking why Panthers fans aren't the ones buying those same tickets.
If you say to yourself "I'm not spending any money to go see the Panthers", THEN YOU ARE PART OF THE PROBLEM. If you are one of those people who say "If I had Panthers' PSLs...". STOP RIGHT THERE. The Panthers are actively selling PSLs. I believe there was/is an advertisement for PSLs as low as $20/month. Go sign up. Are you hesitant to sign up because the Panthers suck right now? Fair. But don't complain about the number of opposing fans in the stadium then.
The product on the field, and the lack of perennial success (the Panthers still have not had back to back winning seasons. Ever.) combined with the fact that the Panthers have only been around for ~25 years all contribute to the current situation.