It's gonna sound like I'm in favor of these measures, even though I am not. I've always tried to reconcile this extra airport "security" with actual freedoms as stated in the Constitution. Meaning are my freedoms under assault here, or am I just whining about a significant inconvenience?
Still, we can't prove a counter-factual. If it never happened because the terrorists didn't try, we have no way to know if it was the security measures or something else. And that even assumes that they would have otherwise tried something, which we don't even know. We think short term, as in a few years at most, while they think long term, decades or even centuries.
They could be planning something that will hit us as hard as 9/11 did, but has nothing to do with airports. Sadly, an open border with so many military age males streaming into the country, does not give me a feeling of security, no matter what happens at the airport.