GXER
The decision to impose a "2 in the cockpit at all times" policy is, though understandable, a thoroughly "knee jerk" reaction by authorities etc. who "have to be seen doing something" - no matter that it only complicates the situation & does not, necessarily , do anything to increase cockpit security.
It is, for the reason that it does not guarantee anything effective to avoid or overcome the problem, & for the fact that it was hastily (& unthinkingly) set up," Kneejerk".
It is unthinking because 1) it introduces another person to the cockpit (who might, in fact, be the perpetrator of this kind of action), 2)that person may be physically unable to overcome the remaining pilot, 3) that person is totally unqualified to recognise a problem caused by the remaining pilot's actions 4) &, unable to take corrective action, 5) make matters worse, 6) far from your simple explanation of being able to open the door for the returning pilot- be totally incapable of doing even that.
Indeed, I should imagine that such a person's presence & influence would be limited to a very slight deterrent to a pilot with such intent.
What do you really expect a lady stewardess, or a weakly built steward, or a lady pilot to physically be able to do to stop a more powerful (& technically capable) pilot from doing what he is suicidally bent on doing !?
The only way a third person in the cockpit would be reliably capable of stopping such actions would be if HE was a type rated, physically superior, pilot ( & then preferably if there were 2 of them - one to overcome the "suicidal pilot" & the other to correct his actions & fly the a/c).
Otherwise, forget it !
These sort of problems need calm, careful, reflective & exhaustive examination & problem solving to overcome. The whole history of the reaction to this terrible disaster & the piecemeal release of information by the investigators have complicated the very investigation that is taking place. It may even have jeopardised an eventual objective outcome ! (By releasing facts & info. ehich should not be in the public domain.
Certainly, I prefer the DLH Chief Executive's more measured approach & reaction - even if he may have appeared a little insensitive at times !