The purpose of screening:
Whatever it is for, it is not to stop terrorists. Consider what would happen if there were a couple of terrorists in line for security at, say, LAX. They are armed, have some knives and maybe a couple of hand grenades. They are fanatics and don't care if they die, so long as they take some of the Great Satanists with them.
What a perfect opportunity has been presented to them! Hundreds or more targets, none armed, all civilians, helpless! The terrorists' mouths must be watering!
Then the screener stops one of them, and says "Oi! you can't take that there great big gun onto the plane with you! Give it here!"
Use your own imagination for the rest, but next time you are flying, look around for what armed response is available, and ask yourself how they would manage to get through the press of panicked passengers to take these guys down. Talk about carnage. But wait, this is the same lot who plan to handle a hijacking of a 747 with an F 15!
Truly, anyone who buys into this garbage cannot have given it any thought at all. But rest assured, terrorists are not stupid enough to risk everything by carrying guns and knives. They don't need to, as they and other hijackers have demonstrated. Passing through security is easy, and there are plenty of ways to impose one's will on a terrified planeload of passengers without computers, nailfiles, exploding shoes and the other THINGS that security is so concerned about. So long as airport security is looking the wrong way, terrorists have nothing to fear. Airport security is a deterrence? Give me a break.