I agree that U2 fans can be very respectful and courteous. I hope you're right but I also think people will be very excited and emotionally charged. This is the biggest band on the planet and this is their first show in 4 years. The hype and excitement are enormous, even two weeks prior. This combination of circumstances to me increases the chances of people ignoring their better instincts and making a mad rush to the door at 8:59am. This is a safety risk and one that in my opinion will be increased by this security policy. (then again, I don't know San Diego ro the neighbourhood.) If they have the security resources to patrol the arena and surroundings to discourage people from hanging around, I don't see why they can't put those resources into arranging a safe GA line-up situation and avoid chaos, pandemonium and injury the next morning.
Strict enforcement may not always be the safest route, especially when reasonable alternatives can be arranged.
Further, I wonder if the people arriving at exaclty 9 will have any interest in joining an unofficial numbering system when they can just run to the door? They will be the ones with the most to gain by starting a charge and it only takes one.
Keeping my fingers crossed.
Jon