We are focusing too much on the terrorists that want to take control of our aircraft and use them as a missile. What about the other possibilities?
Are you going to sit behind your nice armoured cockpit door while these people do something which will cause loss of the aircraft and passengers? (Possibilities not mentionable in print). All the armour in the World will not protect you from the 35,000 foot fall. At some point you may have to decide "If I do not do something we are all certainly going to die, so therefore I am going back to try and DO SOMETHING to prevent the otherwise inevitable". To do anything useful you need to possess superior force. If anyone objects to the carriage of firearms or is afraid of their own capability to use a firearm no-one is going to force them to so. Somehow, threatening a terrorist that you will have a policeman meet the aircraft on arrival at the gate just does not seem to cut it.
ARM THE PILOTS
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It's not the falling that hurts etc. etc.