Covenant,
Looking back I see that I implied, but did not expressly state, that a solid door with a locked during flight regimen would need to be in place. Without that, yes, I agree with you.
Peaople have commented on this thread and others that, for a variety of reasons, a reasonably sturdy locked door will not prevent terrorist entrance to the flight deck. Due to the public nature of this forum I am not going to get into detailed discussion on these point other than to say that every problem I've seen mentioned so far is solveable.
CPB