Let's assume that the TSA's procedures at the security check points are effective. That is, they can detect the danger associated with a single event -- a gun, a knife, an explosive. Perhaps they can detect the dangers associated with a small set of correlated events occurring during a small time window. But what about a very large set of apparently-random events over a very long time window?
As many passengers do, I checked-in online. I was without a printer and so was unable to print the boarding-pass. I have done this before and so knew this was not a problem as the automated kiosks at the airport will re-print it. Obtaining a boarding-pass is an anonymous act.
The boarding-pass is a complex document with many associated facts: the bar code, the passenger details, the flight details, etc. This set of coordinated details is challenging to forge. Solving a crossword puzzle is easier than making one.
The TSA uses none of this complexity at the checkpoint. The checkpoint just checks that the name on the boarding-pass matches the name on the driver's license. In a photoshop-world, how hard is it to make the name on the boarding-pass match the name on the driver's license? Creating 10s or 100s of such altered boarding passes would allow these 10s or 100s of non-passengers into the gate area.
These 10s or 100s of non-passengers don't stay in the gate area. They enter and shortly thereafter leave. The TSA doe not check the departing passenger's legitimacy of being in the gate area. Why bother to check people leaving the airport? What damage could they do?
The damage comes from the result of a large set of apparently random but actually correlated set of events spread over a long time window. Why bother to fabricate your weapon outside the gate area when you can fabricate it inside the gate area. Bring it in one spring, one plate, one activator, one chemical, etc per non-passenger over several days.
It took me less than an half-hour waiting at my gate to formulate this scenario. I hope the TSA already has this covered.