While the author is mostly correct, he fails here. The security system worked as it was designed to do. It kept the terrorists from having guns and bombs. The failure was not of the security system, but of the VICTIM COMPLIANCE POLICY. The terrorist were able to be successfull in their attack because the government has been preaching for 30 years:GIVE THEM WHAT THEY WANT. DO WHAT THE SAY. DO NOT RESIST. LET THE AUTHORITIES HANDLE IT. That is the policy that failed.
The proper response was shown on the 4th flight, the one where passengers foiled the plot. The security of the aircraft should be based on an armoured and defended crew compartment, and passengers knowledge of their responsibility to subdue hijackers.