Maybe you can sneak a blade through, but you're not getting on board with a gun. Maybe you can stick forty grams of plastic explosive up your butt, but you're not getting on board with a bag full of TNT. The 9/11 hijackers used shitty weapons because it was all they could get on board -- they changed the rules, and now they're stuck with even shittier weapons. The shoe bomb was a crappy bomb, and the underpants bomb was even crappier.
Now, if your point is that a terrorist would have to be stupid to even try to attack an aeroplane when so many other opportunities for killing folks exist... then you'd be right. But that's exactly the kind of stupid that terrorists seem to be... they keep on going for the aircraft rather than the crowded music festival. And hey, if they want to keep going for our best-defended rather than our softest targets then I'm not gonna try and talk 'em out of it.
Perhaps the TSA is really a desperate cry of "Oh please don't throw me in that briar patch!"
The former seems pretty sensible to me, the latter seems a bit crazy.
I guess the other problem is this: there's no doubt a bunch of Al Qaeda-ish folks sitting around right now plotting how to kill people. A big sudden announcement that "guess what? you won't have to take your shoes off any more" might just give 'em the idea.