Lawman,
To begin, it’s not like we have lots of data points on such events. The variables involved probably make such an event so unique that assuming there is one good option to resolve it is not valid. There may be nothing that can be done in some cases to significantly improve the outcome.
At least one other person has mentioned this, but it appears to be worth repeating. When aerospace vehicles get shot down, they don’t turn into harmless confetti and flutter to the ground.
Since there were so many potential victims in close proximity to the flight path of this aircraft, there’s absolutely no guarantee that a shoot—down attempt wouldn’t have made things worse. Removing any chance of the aircraft remaining under the control of this individual who indicated he had no desire to hurt others by shooting it with air-to-air weapons certainly wouldn’t ensure it crashed somewhere desireable. Missiles don’t always hit what we shoot them at either. Setting up a shot geometry that ensured a wayward missile wouldn’t hurt someone on the ground may have been difficult, if not impossible. A mach 2+ unguided missile with a live warhead schwacking someone’s house or dropping into one of the venues you mentioned wouldn’t be any better than the possible outcomes you’re concerned about. Opting to gun him might have reduced the radius of potential problems from the inevitable rounds that didn’t find their mark - but they’re still going to fly for several miles once shot. Based on your description of the area, it doesn’t sound like raining several hundred rounds of 20 mm HEI over the surrounding area would have been a good option either. It’s also a bitch to gun an airborne target that’s flying relatively straight and level at low speed. “Safe” shot geometry with the gun would have probably been even more difficult to set up and execute without risk to those on the ground than a missile. There’s a reason we test and practice with missiles and guns at White Sands or in large, over-water Warning Areas.
This is not an ROE problem. Making the choice to shoot him down over a population center is almost always going to be the lesser of two evils. Both options carry enough risk that it’s probably a coin toss. Once he lines up on a target with intent, the shot may diminish the result but definitely doesn’t guarantee no loss of life or property. Think about the second 9/11 airliner hitting the tower and what was in its path leading up to impact. If an F-15 was there to pump a couple of missiles into him and halt that attack a few miles short of downtown Manhattan, that obviously would have been great. But, the crash site was going to be a mess, with plenty of casualties and damage. A lesser “evil” for certain, but still an evil that wasn’t warranted in the Seattle case because the same threat wasn’t indicated to those observing and speaking with the individual involved.