I feel bad for the 150 lost souls. However this, like 9/11, was an extremely rare occurrence.
Now they're going to do the exact same thing they did then - spend hundreds of millions (possibly billions internationally) to make the cockpit "safe". Which, as Fitz alluded to, would have to be nearly the opposite of what they did to make the cockpit "safe" from terrorists. If they switch to allowing coded entry from outside the cockpit again, then of course they make the cockpit vulnerable to a terrorist who has tortured or otherwise coerced air crew into giving them the access code into the cockpit.
I don't see how they're going to provide the safety they're looking for to cover all potential threats. Unless they decide to put an armed Air Marshall in every cockpit. Of course then they'd better make it two, because one of them could flip out.