Geez, I wish I had enough time to write all that's in my head, but I don't. but to hit the high points:
1. Sustainability is about being able to survive and thrive without depleting or destroying the resources you have available. Disc golf sustainability, therefore, is about making sure there are places to play now and in the future, allowing for the expected /desired growth of the sport.
a. Safety is part of this - if people who are bystanders in public parks are being injured, that's bad for sustainability, because courses will be pulled from public parks.
b. Space needed for courses is part of this - when discs fly farther, you need more space for courses. Needing more space means more cost, less availability of land for courses. High costs will slow development of new courses.
2. Disc golf in it's current form is dangerous to unknowing/unaware bystanders. People walking through the park, not knowing there is a disc golf course present have no idea they could be hit by a sharp, heavy projectile thrown hundreds of feet away. This problem has only be exacerbated by advances in disc speed/distance. When I designed my first course in 1985, you only needed to worry about park users, say, 50 feet off the fairway being hit (by blunter discs, too). Now that discs (often thrown by unskilled players) can go even farther off course, you really need 100ft or more of safe space surrounding fairways.
3. Other sports have limited the "wow" factor of their product in the name of safety: baseball bats have been deadened to protect pitchers, racing cars have been made slower to protect drivers and spectators, golf balls have restrictions (mostly to keep courses from getting too long) that make them safer, football requires helmets, makes safer helmets, restricts types of hits. All of these sports remain popular spectator sports.
4. Wide-rimmed, fast, sharp-edged drivers do more damage to trees than midranges or putters. Look at trees close to the tee of a long hole, compared to trees next to the tee of a short hole. Which trees have received more damage? Yes, the trees near the driver-disc hole, not the midgrange/putter hole.
5. Public park courses are part of the sport and part of the history of the sport. Requiring private land and pay-to-play for *all* courses will eliminate most of our available placers to play and make it difficult to get new ones.
6. You don't need heavy, wide-rimmed drivers to have interesting, entertaining, compelling disc golf competition. There were lots of oohs and aahhs when Sammy Ferrans threw his Aero 400+ feet to park hole #4 at Ellison park in Rochester during the finals of the 1984 PDGA Worlds. If all competitors have to "disc down", the competition will still be great.
7. While restricting driver speed/width/sharpness would hurt sales of already-produced discs, those sales would be replaced by increased sales of slower discs, both from existing players and the new players who would come along in the future. Titleist has to make all of their golf balls the same size - they do just fine.
8. A standards change would never happen immediately, but would undoubtedly be phased in over time. X number of years before *any* discs are illegal, with more "old" discs made illegal each year, starting from the fastest/sharpest and adding more each year. It may take several years to do this, but it would get the desired result and give players time to wean themselves off of these discs.
9. Harold Duvall, who made the presentation to the PDGA board, is a multi-time World Champion and has been playing disc golf and other disc sports for well over 30 years. He knows a few things about flying discs. He LOVES the sport of disc golf, which has provided himself, his friends and family with income for 30 years. He is a man of high integrity, and has done a tremendous amount to further the sport of disc golf (creating EDGE, USDGC, donating many courses and countless discs and baskets). I find it hard to believe he would make this proposal without careful consideration of its impact on the sport.
10. Just because Harold is a part-owner of Innova doesn't mean this is an evil Innova scheme to kill the competition. There are people in this world who do things for reasons other than personal financial gain. Harold is one of them.
I'll stop at ten, but I could easily give you many more points, but work beckons.