Defenders of the TSA nudie scanners and enhanced pat-downs keep pointing to public opinion polls showing strong support for the new measures. Nate Silver explains that expressing support to pollsters is one thing, bearing that support out in deciding whether or not to fly is something else.
In the past, more cumbersome security procedures have had deleterious effects on passenger demand. A study by three professors at Cornell University found, for instance, that when the T.S.A. began to require checked baggage to be screened in late 2002, it reduced overall passenger traffic by about 6 percent. (You can actually see these effects a bit when looking at the air traffic statistics: passenger traffic on U.S.-based airlines dropped by about 6 percent from the fourth quarter of 2002 to the first quarter of 2003 — greater than the usual seasonal variance — even though the economy was recovering and travelers were starting to get over the fear brought on by the Sept. 11 attacks.)
More stringent security procedures, in essence, function as a tax upon air travel, and produce a corresponding deadweight loss.
And not just economic loss. Opting to drive instead of to fly is to opt for a more dangerous form of transportation.
According to the Cornell study, roughly 130 inconvenienced travelers died every three months as a result of additional traffic fatalities brought on by substituting ground transit for air transit. That's the equivalent of four fully-loaded Boeing 737s crashing each year.
If the TSA procedures were nabbing terrorists at a rate suggesting they were preventing anywhere near that many air attack deaths, they might have an argument for the procedures. But there's no evidence for that.