here is one for mythbusters.
Myth: General aviation airports are incapable of self security and general aviation aircraft could likely cause damage to high rise buildings on a similar scale to september 11th.
I'm not sure how relevant this comparison is as I couldn't bear to watch more than a few seconds of that video clip. I think you have to be very careful when attempting to debunk these statements. I'm on your side but could take issue with several of the points you're making. I'll concentrate on what I think is the most important.
You have to appreciate that we are now faced with a new kind of terrorist (for want of a better word). These people are so convinced of their beliefs that they are prepared to sacrifice themselves to achieve their aims. This means remote controlled weapons don't come into it. They are the guidance system & part of the bomb themselves which makes things so much easier. The main point of the argument is that it would be so much easier & far more effective to do this with a car or truck bomb than with any form of light or GA aircraft. With the will & determination to actually carry it out almost anyone could do it without needing to learn to fly first.
Unfortunately, once something has been done there's no going back. However unlikely the threat actually is, the possibility of another 9/11 will always be with us. There is also the risk of some nutter getting the idea into their head & having a go themselves. The terrorist organisations know this only too well & take full advantage of it.