(b) The pilots were not charged with a crime, they just got real embarrassed (as they should be)
(c) The plane could have contained lots of dangerous chemicals. Why wouldn't anybody think terrorists couldn't use a very small plane to do a nasty job?
(d) I agree that this event with the small plane could be a diversion from a larger attack, but you have to react to what you see in front of you at that moment. If somebody is running towards me with a knife, I'm not to going to spend time looking over my shoulder to see if another guy is also attacking me with a knife from behind. I have to first take care of the threat that is known, and in front of me.
The small plane incident was handled pretty well, very well. What is not so well is all the panicky caterwalling after -- the attacks on civil aviation, specifically.