PGA rule for their competitions, not USGA rule of golf.Is there a specific rule that says you must walk? I found references to things like "as a general rule..." but nothing concrete such as "Rule 13.2.b states players must walk..."
The Martin case was back in 2001. How many players have you heard riding in carts since then? I've heard of zero. It was also for Q-School which was famously physically demanding. He was also good enough to compete but needed a cart due to a physical disability. The USGA has a provision for players with disabilities but ADA protection is going to trump other rules every time.
As for John Daly, he requested the cart because he has arthritis in his knee, not because he's fat.
ADA shouldn't trump private voluntary competitions, IMO. That's not how freedom should work. That's my argument. Obviously the courts disagree with me. If he wants to create another golfing association where people can ride carts, or play blindfolded, or use golf ball cannons or whatever rules he wants to imply, then please, feel free. But forcing a private entity to allow you a competitive advantage? That's wrong. Again, IMO.