I do not understand the confusion about the door discussion.
Rationally, the situation is very simple: there is a high degree of (anti)symmetry between 911 and this case. It also does not make sense to look at death counts:in a Bayesian sense the posterior probabilities for this case are at least the same and probably worse. This guy could have flown into a sky scraper if he would have chosen to do so, just as many non-911 hijackers chose not to. One can even argue that a professional pilot will be far more effective at killing given that the person up front, pilot or hijacker, chooses to. The 911 event was peculiar in a sense that the hijackers actually were (partially trained) pilots with some (quite a bit actually) effectiveness in crashing the plane. Surely one of them at that time could, in principle, have made it into the cockpit professionally but with with evil intent.
Given this symmetry, the question then becomes one of anterior probability: what is the likelyhood of a hijacking vs the likelyhood of pilot mass murder, given that the latter may have an even worse outcome. This is measured purely on a 'number of events' basis. I think that the easy way out that many propose, stating that one is negligible with respect to the other, has no basis in reality. Therefore 'door mechanics' is an important part of this problem and the system does need modification.
The 'CC on FD' can help in certain cases but it also opens a whole new set of issues that should be properly evaluated before a good system can be designed.
The solution to this issue should be one of carefully weighing 'knowns' without introducing adverse 'unknowns'. A rush to judgement will turn out to be counterproductive.