It was obvious years before 9/11 that airport security was a problem. George Carlin did a 5 minute set about "Airport Security" in 1998 or 1999. He even mentioned many of the things that the hijackers used.
Security won't really be improved until something else drastic happens. The cockpit door was the best step. Screening everyone the same, would be the next one. Letting employees through without the same check is just silly.
I won't even talk about cargo that isn't screened. It's all a game to make the Kettles think they're safe. I could take a class of junior high students, and could come up with at least 5 ways to smuggle prohibited items on the plane.
When I'm out of the US and traveling for a month or so, I loathe coming back to the US and the screaming and often rude TSA folk. They're not all bad, and I understand they're just doing their jobs. It's all security theater, though.