Anthony, while you might be right in theory that a large enough group of burly terrorists could overwhelm a small enough group of pax, in practise there is another factor at work to consider (other than the door barrier). 9/11 didn't happen just because of a passive pax response, it also happened because of poor intelligence at several levels. Passenger lists are now much more dilligently screened, analyzed, and cross-referenced against intelligence data and/or known risk factors. Cash purchases, last-minute purchases, one-way ticket purchases (and combinations) now raise eyebrows. Therefore, as a terrorist group attempts to increase it's numbers in boarding a plane, it also increases it's risk that one of them will be red-flagged. Numbers work AGAINST them, not FOR them. I really don't think you're going to find a large terrorist sleeper-cell of squeaky-clean individuals without backgrounds. Remember, even in the days pre-9/11, when intelligence was clearly lacking, there still WAS data on most of the guys involved in that plot.... it just went unused.
I agree with Tan... there is a 'new reality' of aviation security, that aviation authorities don't seem to grasp. Really, the best counter-terrorism device is imagination. Finding ways to counter what the real threat (in other words the NEXT threat) is. It boggles me that aviation security can't understand this, and be a little more proactive.
I have my theory on this mentality. I think security and military types, police even to a certain degree, share a lot of common thinking. One trait is a sort of self-righteousness in their actions, that prevents them from ever changing course or trying new ideas. The psychology is that if they ever changed something, it'd be like admitting to themselves & others that they've been wrong, which would undermine their status as ultimate authority. Power not only 'corrupts, absolutely', it also 'corrupts the mind, absolutely'. It does a lot to destroy creativity and the ability to self-critique.
You see symptoms of this thinking in the militism seen in things like the Palistinian-Israeli conflict... where after dozens of years of conflict, they STILL believe that if force/violence doesn't work, the solution must be just MORE force/violence. Or in the U.S. "war on drugs" where for decades of the same style of drug-raids, drug laws, enforcement methods, the only answer they have to none of them working is to have MORE of these same things.
The psychology of this self-importance naturally leads mililtary/police types to always choosing the solution that increases their role, their financing, their job security. It can become an unstoppable animal. For every terrorist act that will now ever occur, the military can just say "We need MORE military spending to stop this!!"
But back to the point, now you have aviation security thinking because some small sharp knives were used by one group of terrorist on one day.... the solution for the future must be ... find all small, sharp objects! No nail-clippers allowed! Brilliant! Or you have the U.S. military thinking " we couldn't shoot down those planes" so the solution: fighters in the air non-stop, we'll definitely get them next time! Thing is, there WON'T be a next time the same way that it happened LAST time! Just think of how those military bucks could have been spent.
Not only are things like knives ineffective in the new reality, but regardless, tests of aviation security show that at ALL airports, security scanners let through most knives, guns, x-ray blocking bags, anyways. It's natural, if you think of the 2-dimensional images you get from an x-ray machine. These things can have any odd orientation in the baggage. But instead of realizing the human/technological limitation at security points, and devising new ways to get around that, or defeat new threats, the solution is fire the scanner if anything gets in the press.