These doors very effectively mean that control of the plane would be put into the hands of the cabin crew, but magnifies the cost of a rogue operator -- I am certain the risks were evaluated and the challenge of a determined suicidal pilot was ruled outside scope. And yes, there are emergency override codes, but there are also time override-overrides from within the cabin. Even if the protocol where two members of st…
Or to put it in a more general way: is security theatre now costing lives?
Historically, hijackings are more deadly than rogue pilots. Neither one is a particularly big threat, but hijackings are the more important threat of the two. How many potential attacks from the past decade and a half got stopped in the planning stage because "Well gee, Bob, that sounds great, but how are we going to get into the cockpit?" While this stuff is rare, I bet it's not zero.
Beyond that, does not having a locked cockpit door actually save you from rogue pilots? I don't think so. There's a lot you can do to defeat other people when you're the only one belted in at the controls. A series of violent vertical maneuvers would suffice to defeat anyone trying to get back in. Imagine if, instead of locking the door, this guy had just pushed the nose over to negative two gees, then pulled up at positive three, repeat until everyone is dead? Or, pull the breakers for the higher-level fly-by-wire systems, point the nose at the ground, apply full throttle, and rip the wings off? The thinking seems to be that there was a calm 10 minutes or so in which he could have been stopped if only the door hadn't been in the way, but the only reason there was a calm 10 minutes was because the door was in the way.