Just a thought, have read some of the thread and can see how this happened fromt he very detailed explanations, but, am I right in saying that the incident would not have occurred in the pre 9/11 world as the cockpit door was not locked back then so the door would just be opened manually by the returning crew member ?
Potentially, to my mind, if that is the case this would be an indirect consequence of 9/11 and the changes that were made, sort of a bit like how Burglar alarms and Anti Virus Software seem to cause as many problems as threats they solve but in a much more serious way.
Would it have gone that way anyway regardless of the terrorist threat ?