I can't agree with any of this.
To start, we should not be relying on a terrorist's ignorance about our protocols or inability to act normal while going through security in order to detect him. So the idea that it was "easy" for these agents to slip through because they knew the system or weren't legitimately nervous is wholly irrelevant.
Secondly, I have no idea why a terrorist would be more deterred by the countermeasures he's aware of as opposed to the ones he isn't. By definition, he can't be as prepared for the behind the scenes security.
And to further the point about the importance of behind the scenes stuff...while this story is shameful and sad, it's not as if there aren't other layers of security to help keep us safe. Still though, for as much money, time, energy, and annoyance on the part of travlers is expended at these TSA check points, they have to do better.
I'm for the behind the scenes stuff also. Having both is definitely more effective than just having one or the other. The process just doesn't annoy me like it apparently does most of you.