Here I was, thinking that the security checkpoint was a measure to make everyone feel safer. Thanks for clearing that one up!
"An attack looks like it will take so much effort that the terrorist is no longer interested (terrorists are lazy, too) or capable"
Except that you can buy or obtain all the things needed to kill people on an airplane on the other side of the security check. You can buy glass, you can get knives from restaurants, etc. The fact that you get a security check long before you are anywhere near an airplane leaves a lot of room for an attacker, even a solo terrorist who is not particularly creative.
Note that the Israeli approach involves walking up to the door of an airplane without any carry-ons or shoes. Profiling is needed to determine who is even worth the attention (if they did that to everyone, there would be riots). Meanwhile, the TSA will let you bring a pocket knife onto a plane, which is more than enough to kill people.
The real difference today is not that terrorists have a harder time bringing weapons onto planes, but that passengers and crew do not believe they will survive a hijacking. People will now fight back. The locked cockpit doors -- locked from the inside -- help a lot too. Any security beyond explosives detection is pointless, and you could have that sort of security right at the departure gates.
I personally doubt that the TSA checkpoints were ever meant to keep us secure. The Bush administration just needed to reassure people that we would have better security than we did beforehand, in a visible and easy-to-understand way. Now the agency is huge and no politician can afford to void against checkpoints, just in case a clever terrorist manages to hijack a plane (or perhaps shoot it down with a surface-to-air missile; people would probably blame lax airport security in that case too). It also helps that so many contracts are awarded for building the TSA's equipment, and that the TSA has substantially weakened Americans' ideas about civil rights (and what mainstream politician will complain about such things?).