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Might work, but you'll still need someone to operate the system. Who would that be? The pilot? The flight attendants?
Where would the button be? If we put it outside the cockpit a rogue passenger could eject everyone. If inside, it would make it easier for the pilot to kill everyone without crashing the plane. He'd just have to push it somewhere over the Arctic Ocean and they'd be all dead of hypothermia within an hour.
The solution to this new wave of maniacal use of the heavy locked door to the cockpit is to simply mandate that it be unlocked.
Then any crazy or religious-crazy pilot or copilot would have to deal with the passengers not being inclined to participate with the crazy.
Crazy passengers would have to deal with the other passengers.
Majority would rule.