It's obvious that these critics do not have any understanding about the resolving of the target solution in an air defense problem. IOW's, when the bullet gets to where the the aircraft was when the shooter shot, the aircraft will not be there. The aircraft has moved on, unharmed and will continue to do so.
Well, if you had 1,000 Barretts lined up, SOMEBODY would have to hit it, right? But then I guess the terrorists, lacking 1,000 men, would say "Let's just call Muhammed and have him send us a machine gun and bring it in from Mexico on the back of illegals". Then Abdul would say "Muhammed, you silly man, for that kind of money we can get a shoulder SAM from Saddam!" Then Muhammed would have to tell Abdul the bad news about Saddam.
--as an aside to this, in both the European and Pacific theaters of war in WW2, approximately 12000 rounds of .50BMG ammo were expended per enemy plane shot down--and that was trained, aimed shooting--
True. I gather that they think that airplanes are a good deal sturdier than they are, as well. A lot of aircraft can be penetrated with a screwdriver and a forceful stab. Airliners and corporate jets can be damaged- assuming you could hit the thing to begin with- by virtually any small-arms fire.
But then, a lot of jouralists are far to busy doing more important things that doing their homework or finding out what the facts are. They're raising awareness.
I'll bet I could come up with a computerized mount that would do the job. Still couldn't get a real high Pk, but maybe enough.
Of course anyone with half a brain, letting out most of the terrorists, would go after aircraft stoped in traffic on the taxiway, or coming around to the active just before takeoff. Of course you could do just as well, better really, with a large game hunting rifle, in terms of punching holes in fuel tanks, especially the little feeder tanks by each engine, or punching a hole in the hot section of a spinning turbine, the latter would have "interesting" secondary effects I'm sure.