Interestingly enough some high ranked security officials in germany are now talking about removing the door again as the safety case is not as easy and one dimensional as originally thought.
I can see some sense in this. Currently if hijackers gain access to the cockpit they can lock themselves safely inside until they destroy the aircraft. However, now that passengers realise that their death is almost certain if they take no action it is more likely that they will attack the hijackers en masse and the removal of the armoured cockpit door would facilitate this. Sheer numbers will overcome the hijackers - just hope there is a dead-heading pilot on board.
Pretty certainly a weak cockpit door could have helped in the recent situation but only because the aircraft was an Airbus with flight envelope protection. (Disclaimer, since I never flew the 'bus I do not know how effective the system is). Quite likely, on an aircraft without this protection the wayward pilot would simply have rolled the aircraft upside down and it would have been game over.
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