All of this ignores that the problem is the cockpit door. If the pilots had a separate door from the outside, and there was no passthrough between the bulkhead aft of the cockpit, it would solve the highjacking problems for good. There could be a bloodbath in the passenger compartment, but it would accomplish nothing.

Of course, this would amount to an admission that the pilots are just bus drivers and having them crawl around the passenger compartment to fix or diagnose a problem (like they supposedly did in the old days) is just fantasy.

A small, armored, pass-through door like a revolving darkroom door which is only controlled from the cockpit would be all that is necessary for them to get everything they need from the passenger cabin -- a cup of bad coffee.

Oh, they wouldn't be able to stand there stupidly and say "good day" to everyone as they leave. Too bad.