The eloquent statements made by people much closer to this tragedy and its root causes than I am prompt me to consider how we should deal with one of its effects: not just the crash of the four airliners, but the crash of the airline system which followed.
I suspect that the 9/11 events will be remembered like the Hindenburg disaster of 1937. Although modern airliners are rugged, proven, hard-working and highly-evolved craft, the air travel system as a whole has become fragile, overextended, and subject to spectacular failure. 1937 signalled an end to the era of airships and led directly to our current airline system; 2001 may signal an end to the era that began in 1937 and the beginning of something else.
Technologically, there are many solutions to the problem of high-speed transport besides airliners. Most are variations, one way or another, on the principle that it is inefficient to build machines that fly above most or all of the atmosphere to achieve high speeds when you can simply remove the atmosphere from a small tube on the surface and send whatever you want, exactly where you want it, at almost any speed you wish.
In addition to technology, there is topology. Our hub-and-spoke airline system was near a breaking point, and adding a 2-hour delay in getting through an airport that then gets you to another airport that is still 2 hours from your destination could be the final straw that gives alternatives a chance. Think packet-switching of 6-passenger capsules rather than circuit-switching of 200-passenger planes.
A new network won't begin to grow until it is given a critical mass from which to start. ARPA had to get the Internet started with those first few nodes. Don't throw good money after bad trying to bail out the airline industry; put that money into something else. Get the oil pipeline industry, Boeing, Detroit, and all defense contractors on board. The United States deserves an internal transportation system commensurate with its stature as the leader of the free world. This war will be won on the ground, not by trying to defend against rogue missiles, rogue airliners, or rogue states.
How did the United States of America win the cold war? It wasn't by building Intercontinental Ballistic Missiles. It was by building the Interstate Highway System.