One apparently knowledgable poster has made the point that the purpose of the screening is not what you think it is.
What other purpose might it have?
To convince passengers that flying is safe? If so it isn't working. Pax can see the obvious flaws in "security" screening just as well as the posters here.
To deter terrorists from even trying to hijack a plane? Ditto. Anyone with any inteligence who thinks about the issue will come to the conclusion that hightened levels of security checks do little to increase safety.
To cover backside of politicians and administrators in the event of another terrorist attack? This, i think, is at least partly true.