I didn't read through the whole thread. So, I hope I'm not repeating what others might have said. If I am, I apologize. Here's my 2 cents:
Obviously, this is to prevent another 9/11. By having firarms, those pilots who flew the four hijacked planes on 9/11 might have had a chance to change the outcome. However, 9/11 does not happen all the time. It took those terroists few years of planning and training to pull it off. Better intelligence would have averted the disaster. By allowing the cockpit crew to have firearms, I'm afraid it would increase the possibility of some lunatic, suisidal pilots to do something drastic. In the past five years, we had at least two, namely, Egyptair and Silkair. I honestly think this is a very dangerous policy.