The real error is that it assumes the primary role of TSA screening is to prevent attacks. Looking at the record, their primary job is to catch really stupid drug dealers, drunks, and people subject to federal warrants. That's the vast magority of arrests and is little damaged by pre-screening. Enforcement of terminal drink/food monopolies is just a bonus.

This is security theatre. Trying to apply logic doesnt work. There was a report a few years ago, accidentally leaked, by TSA showing that 911-style hijacking was no longer possible. Nobody with small knives could ever take a cockpit, not with 100 post-911 passengers watching.