Since 9/11, our nation has been obsessed with air-travel security. Terrorist attacks from the air have been the threat that looms largest in Americans' minds. As a result, we've wasted millions on misguided programs to separate the regular travelers from the suspected terrorists -- money that could have been spent to actually make us safer.

Consider CAPPS and its replacement, Secure Flight. These are programs to check travelers against the 30,000 to 40,000 names on the government's No-Fly list, and another 30,000 to 40,000 on its Selectee list.

They're bizarre lists: people -- names and aliases -- who are too dangerous to be allowed to fly under any circumstance, yet so innocent that they cannot be arrested, even under the draconian provisions of the Patriot Act. The Selectee list contains an equal number of travelers who must be searched extensively before they're allowed to fly. Who are these people, anyway?

The truth is, nobody knows. The lists come from the Terrorist Screening Database, a hodgepodge compiled in haste from a variety of sources, with no clear rules about who should be on it or how to get off it. The government is trying to clean up the lists, but -- garbage in, garbage out -- it's not having much success.

The program has been a complete failure, resulting in exactly zero terrorists caught. And even worse, thousands (or more) have been denied the ability to fly, even though they've done nothing wrong. These denials fall into two categories: the "Ted Kennedy" problem (people who aren't on the list but share a name with someone who is) and the "Cat Stevens" problem (people on the list who shouldn't be). Even now, four years after 9/11, both these problems remain.

I know quite a lot about this. I was a member of the government's Secure Flight Working Group on Privacy and Security. We looked at the TSA's program for matching airplane passengers with the terrorist watch list, and found a complete mess: poorly defined goals, incoherent design criteria, no clear system architecture, inadequate testing. (Our report was on the TSA website, but has recently been removed -- "refreshed" is the word the organization used -- and replaced with an "executive summary" (.doc) that contains none of the report's findings. The TSA did retain two (.doc) rebuttals (.doc), which read like products of the same outline and dismiss our findings by saying that we didn't have access to the requisite information.) Our conclusions match those in two (.pdf) reports (.pdf) by the Government Accountability Office and one (.pdf) by the DHS inspector general.

Alongside Secure Flight, the TSA is testing Registered Traveler programs. There are two: one administered by the TSA, and the other a commercial program from Verified Identity Pass called Clear. The basic idea is that you submit your information in advance, and if you're OK -- whatever that means -- you get a card that lets you go through security faster.

Superficially, it all seems to make sense. Why waste precious time making Grandma Miriam from Brooklyn empty her purse when you can search Sharaf, a 26-year-old who arrived last month from Egypt and is traveling without luggage?

The reason is security. These programs are based on the dangerous myth that terrorists match a particular profile and that we can somehow pick terrorists out of a crowd if we only can identify everyone. That's simply not true.

What these programs do is create two different access paths into the airport: high-security and low-security. The intent is to let only good guys take the low-security path and to force bad guys to take the high-security path, but it rarely works out that way. You have to assume that the bad guys will find a way to exploit the low-security path. Why couldn't a terrorist just slip an altimeter-triggered explosive into the baggage of a registered traveler?

It may be counterintuitive, but we are all safer if enhanced screening is truly random, and not based on an error-filled database or a cursory background check.

The truth is, Registered Traveler programs are not about security; they're about convenience. The Clear program is a business: Those who can afford $80 per year can avoid long lines. It's also a program with a questionable revenue model. I fly 200,000 miles a year, which makes me a perfect candidate for this program. But my frequent-flier status already lets me use the airport's fast line and means that I never get selected for secondary screening, so I have no incentive to pay for a card. Maybe that's why the Clear pilot program in Orlando, Florida, only signed up 10,000 of that airport's 31 million annual passengers.

I think Verified Identity Pass understands this, and is encouraging use of its card everywhere: at sports arenas, power plants, even office buildings. This is just the sort of mission creep that moves us ever closer to a "show me your papers" society.

Exactly two things have made airline travel safer since 9/11: reinforcement of cockpit doors, and passengers who now know that they may have to fight back. Everything else -- Secure Flight and Trusted Traveler included -- is security theater. We would all be a lot safer if, instead, we implemented enhanced baggage security -- both ensuring that a passenger's bags don't fly unless he does, and explosives screening for all baggage -- as well as background checks and increased screening for airport employees.

Then we could take all the money we save and apply it to intelligence, investigation and emergency response. These are security measures that pay dividends regardless of what the terrorists are planning next, whether it's the movie plot