Airline accidents are very rare because the industry learns from previous mistakes. Many aviation magazines contain accident reports so we can learn from the mistakes of others before learning from our own mistakes. Before Sept 11th, there had not been a single fatal airline accident involving a US carrier in over a year even though there are thousands of flights every day. The last prior US carrier fatal accident that I recall was the Alaskan Air crash back around January 2000.

Some solutions are viable, such as adding an Enhanced Ground Proximity Warning (EGPWS) system to prevent Controlled Flight into Terrain (CFIT) accidents. CFIT is a relatively common accident scenario and a good EGPWS goes a long way to reducing the danger.

You're right about the Rube Goldberg ideas coming out of the woodwork following an accident. Remember the question about purging empty fuel tanks with nitrogen to reduce the chance of an explosion? It sounds like a good idea until you realize it'd cost billions to implement and would only be effective against a very rare accident cause (literally one in several million probability). I remember hearing people wanting to fit big parachutes on planes to lower them to the ground in the event of a problem up high. Hell, if you're going to do that, why not just put everyone into ejection seats? Could you imagine punching out over 400 passengers on a loaded 747?

There are only so many dollars to go around. That being the case, we need to prioritize them towards the most likely causes that can be solved. There are several thousand airliners in the US fleet and many of them are over 15 years old. There's only so much you can do in a cost effective manner to upgrade an old plane but most airlines don't have the money to replace them with newer equipment.

I do agree that we need to step up security both on the ground and in the plane. However, these hijackings were unprecedented. Before Sept 11, both airline and FAA policy was for the pilots to not do anything to resist a hijacker. All a hijacking usually meant was a diversion to some out of the way location and perhaps a few uncomfortable days while negotiations took place. Once in a while, police forces would storm the plane or the terrorists would execute a passenger but in most circumstances, the passengers survived. No more. You can rest assured that any future hijacking attempts will be met with force from both the passengers and crew. That appears to have happened on Flight 93 because the passengers learned via phone calls of the other hijacking outcomes.