The terrorists deliberately chose aircraft from one of the few countries which happens to have a locked flight deck policy.
Doesn't the end result show in the best (or worst, as it were...) possible way, how useless the locked flight deck actually is? I think it is a fallacy, probably even has a detrimental effect from the false feeling of security it induces.
The international community must come up with something drastically better than that weak, and indeed old, idea.