Even a normal bullet passing through the body wouldnt down the aircraft. Yes it would depressurise but thats not a lethal event for a small hole like that.
Im not sure what size hole the planes PAX are rated to maintain a pressure but in any case the standard procedure in that oxygen masks drop, people scream and the pilot dives to 10,000ft. Upsetting yes, deadly? No.
Id be more concerned about a miss hitting one of the other 250 people around the place than anything else.
A few other points - it saves terrorists the job smuggling a firearm onto the plane. Few hijackings are one man efforts, 4 or 5 hijackers could easily overpower a lone air marshall.
September 11th hijackers were all done with small knives and implements not firearms - they didnt need them.
Im getting really sick of this country giving in to every single demand the USA makes of it with this being the latest in a long line of total capitulation.
America is a country paranoid at the moment and unfortunately an imbecile in charge of a paranoid nation isnt exactly condusive to world peace !
I also think a lot of these alerts are deliberately overstated to keep the population scared to keep support for his policies. Some of them also seem to be used in a business sense to put non US competitors at a disadvantage, for example airlines.
Money would be far better spent stopping terrorists getting on or getting a weapon ONTO an aicraft in the first place.
A relative of mine recently flew back to the UK from europe and by accident left his swiss army knife in his camera bag which was hand luggage - it went totally undetected.
On the other hand i must look really dodgy as nearly every time i fly i get my own personal pat-down search.
Out of the 16 or so flights ive made since September 11th ive been searched on 12 of those. The worst being my trip to Venice on first week of January 2002. I wore my thick snow boots as it was sub zero and snowing there only to have to take them off at Gatwick, demonstrate the bottoms werent cut open or hiding anything and have them sniffed (rather them than me...). This was only a few weeks after the shoe-bomber attempt.
Coming back was worse, i cleared security and when they called the flight went through the gate onto the tarmac. At the bottom of the plane steps were 2 italian policemen who took me to a side room where my boots were removed and searched, i was searched and my hand luggage searched to the extent that my electric razor and minidisc player were taken apart. By the time they'd finished the plane had boarded and i walked up the aisle with everyone glaring at me and im sure thinking "Terrorist". Just to add to the paranoia, although the plane was quite full there was nobody seated next to me, across the aisle or the one in front or behind
Anyway.. Ive drifted off topic so to summarise... Guns on aircraft == bad thing