In general terms, why? Airport security is now and always has been a complete farce. That the govt has taken over makes it that much more so.
Since airlines are a public conveyance, operated by a private entity, and are just like trains, buses, and other forms of "public" transportation where is the hue and cry for such security measures there? Such other modes of transportation have the equal possibility for human and materiel destruction, so where are the hours long waits to board a bus?
No security system is perfect, and airplanes, even with armed passengers may still be flown into buildings. That said however, it has been reliably demonstrated that counting on someone else for your security is not a good idea. Guns, knifes and all sorts of other "weapons" are continually getting through the most heightened security that can be offered. In other words, it ain't workin.
It's time to try the one thing that has been proven, over and over again in a myriad of scenarios to work.
The armed citizen.
Armed citizens are nice, but armed citizens are the last line of defense in war, not the first. Make no doubt about it, this is war. These guys want to destroy the country. In every war we've ever fought, even the Revolution, the citizens were the final line. And the problem with this war is that the front is whichever plane these guys try to take, and we won't know the war is even on until it's far too late.
This isn't the hijacking of the 70s, we're not talking about having a hundred people scared and inconvenienced and maybe 1 or 2 killed. We're talking about having buildings knocked down, thousands dead, economy F'd up for months. Hardcore no nonsense acts of war. If we were still dealing with 70s style hijackers you'd be right. But that time is gone. The new time is that we have hundreds of guided missiles in the air at all times and security, layered security that starts as far away from the plane as possible and ends in the cockpit, is how you keep them from going off.