The Economist has been hosting a spirited debate between Kip Hawley, former head of the Transportation Security Administration, and security expert Bruce Schneier, probably the agency’s most prominent (and fierce) critic. The reaction from readers suggest that the overwhelming weight of opinion is with Schneier, who writes:

Exactly two things have made air travel safer since 9/11: reinforcing the cockpit door, and convincing passengers that they need to fight back. Everything else has been a waste of money. Add screening of checked bags and airport workers and we are done. All the rest is security theatre.

Hawley falls back, repeatedly, on the claim that the new measures must have been effective and worth the cost, since there have been no successful attacks on airplanes over the past decade. By which logic my magical tiger-repellant rock is also highly effective—I’d be willing to part with it for a few thousand dollars, which when you think about it, is a small price to pay for peace of mind. As Schneier observes, successful attacks were an extraordinary rarity before 9/11 as well—and academic studies, the excellent work of our own John Mueller—provide no support for the thesis that the enormous expenditures on airport security since have meaningfully reduced the risk. Oddly, neither do any of Hawley’s anecdotes about various foiled plots—which involve admirable intelligence and law enforcement efforts disrupting terror cells long before they get anywhere near an airport.

Schneier concludes with a look at the positive costs of all this questionable screening. If time is money, Schneier estimates that the economic costs of travel delays, multiplied by millions of passengers, dwarfs TSA’s budget each year. Moreover, as those delays—and “enhanced” procedures that sometime seem deliberately designed traumatize survivors of sexual abuse—push travelers into riskier modes of transportation, more lives are likely to be lost without terrorists having to lift a finger. But the most profound cost may be our acceptance of the procedures themselves—and of a society where intrusive searches and arbitrary rules are just a normal part of getting around:

The goal of terrorism is not to crash planes, or even to kill people; the goal of terrorism is to cause terror. Liquid bombs, PETN, planes as missiles: these are all tactics designed to cause terror by killing innocents. But terrorists can only do so much. They cannot take away our freedoms. They cannot reduce our liberties. They cannot, by themselves, cause that much terror. It’s our reaction to terrorism that determines whether or not their actions are ultimately successful. That we allow governments to do these things to us—to effectively do the terrorists’ job for them—is the greatest harm of all.

But one form of TSA screening is clearly highly effective: The agency recognized that Schneier’s arguments posed a clear and present danger to its budget, and successfully campaigned to have him excluded from a recent congressional hearing at which he’d been slated to testify.