They just don't and won't stop.  Here's another one:

For at least 25 years, the Federal Aviation Administration failed one test after another when it came to airport security. Undercover agents walked through airport checkpoints toting machine guns on their backs and bombs stashed in their carry-on luggage. Agents easily breached security precautions, breezing past locked doors to enter empty planes, mingling behind the scenes with ground crews.

...

"The facts remain the facts," says Steve Elson, a former undercover FAA security officer who tried to warn the agency it was on the edge of disaster. "It is still child's play to knock down 50 airplanes in a few hours' span with near 100 percent chance of success, and probably quite easy to fly a plane into the White House or Congress."

I contend it's simply not possible to make airplanes any safer with the current approach.  We need to completely rethink the problem from a clean slate, do some simulations, and reimplement our security based on solid science rather than pandering to the mental disorders and power cravings of a few people.