For all the ones who propagate that the two personas at all time rule in the US has never brought any problems...
Sorry, flawed argument. Until the 10th of September 2001 one could have argued that noone has ever used a commercial aircraft as a weapon and that therefore it will never happen.
The rule in the US is there as otherwise the armoured and locked door is not cerifiable, exactly because a pilot left alone with psychological problems may take advantage of the situation.
The concept of the door is wrong to start with, as it assumed that all pilots are superheroas and will unde no circumstances ever let the baddie into the cockpit under extreme duress. Unless you have ever been under duress you don't know how you would react to it.
The whole system is based on a series of flaws that look good, but in reality are not. Time for a complete (and non public) rethink.