Eh, that's probably more of a trade off. The door is typically going to be unlocked during the flight anyway so the pilots can get their meals and use the head,

Eh, that's probably more of a trade off. The door is typically going to be unlocked during the flight anyway so the pilots can get their meals and use the head, and then you're creating a risk that a hijacker gets into the cockpit and locks the door behind them. Whereas it's already pretty hard for a hijacker to access the controls after the passengers kill them.