This I disagree with.
First, a fighter that goes up to intercept one of your dozen aircraft doesn't have to shoot it down. All of us (pilots) have been taught to recognize the international sign for interception and that if such interception should occur we should follow the intercepting aircraft to a field to land.
Second, the 9/11 planes weren't exactly operating as a confused 172 pilot might if he were IFR and had an electrical failure. The WTC planes were at altitude on a western course 100 miles north of NYC being piloted by very experienced pilots. Such pilots who were really in trouble at that point probably would have headed for Rome AFB. I'm sure that all sorts of alarms went off five minutes after they broke off communicantions and turned south. My understanding is that planes were scrambled, but that they just couldn't get to NYC (from Otis AFB on Cape Cod) in time to do any good.
ML/NJ