I expect we will have to agree to disagree, I would have thought with the captain outside asking to be let in, screaming/panicking flight attendants and passengers (probably visible to the cockpit flight attendant) and the aircraft in rapid descent toward mountains, most flight attendants in the cockpit would take a little more reassurance than you telling them not to let the captain in. Indeed, I would think it would be extremely unlikely now that they would not let the captain in after Lubitz flew the GermanWings A320 into the ground. That's what happens when you have lost people's trust.