The purpose of terrorism, wherever it occurs, is to create fear that is disproportionate to the size of any terrorist risk. As Posner indicates, many people have considerable fear of flying even under the best of circumstances. This fear is increased when there is an attempt by a suicide bomber to blow up a plane, as happened in December on a Northwest flight going from Amsterdam to Detroit. The fear is multiplied several fold when attacks are successful. Air travel within the US, and between other countries and the US, took a nosedive after the 9/11, 2001 successful multiple attacks on planes going to New York and Washington.
Yona Rubenstein of Brown University and I have studied in detail reactions to the terrorist attacks on Israeli buses and restaurants during the Intifada period. We show that bus travel in Israel fell significantly after every suicide attack on a bus, while the use of taxes and private cars increased. Similarly, eating in restaurants fell rather sharply after a suicide attack at a restaurant, and this was partially replaced by take out orders. To attract business, restaurants began hiring private guards stationed in front of restaurants, and these guards thwarted several attempted suicide bombings.
Airlines have to give a similar reassurance to air travelers by providing a level of security that allays many of their often magnified fears. The optimal level of security on air travel is much higher than would be the case if an exaggerated fear of air travel due to possible terrorism were not so prevalent. For this reason, checking of shoes, laptops, liquids, and even body scanners may be often useful, even when they are not so effective.
In addition, greater profiling of passengers would be desirable. After the December bombing attempt, President Obama did order a more careful check of individuals coming from higher risk countries, such as Yemen. That is a step in the right direction, but it is not enough. Young males of Moslem background have committed virtually all the terrorist attacks against airplanes traveling to, or within, the US. They should have the most invasive security checks. Since it is not always apparent who is a Moslem, this profiling would often have to be proxied by country of origin, name, and other such identifying features. Many law-abiding young Moslem males would be offended by having to go through an especially intensive security check, so they should be treated with the utmost respect. It might also be publicized that such intensive procedures would make it easier for young Moslem males to get American visas.
Terrorist organizations would react to such profiling of Moslem males by trying to find substitutes. Perhaps the closest substitutes are religious young Moslem females, and young non-Moslem males who are sympathetic to the terrorist cause. Therefore, these groups should face tougher security checks than other passengers, but not as tough as young Moslem males. Probably the optimal approach would be to inspect a fraction of members of these groups as carefully as young Moslem males, while the other members would be given a less complete check. Other passengers, such as old women and men, and young children, do not need to receive onerous checks. Since the vast majority of passengers fall into low risk categories, extensive profiling of the high security risks would reduce the overall security effort while at the same time increasing the protection of air travelers from terrorist attacks.
I recognize that explicit profiling is unpopular in some quarters, in part because the profiling of African Americans with regard to crime detection and prevention was abused. Nevertheless, making judgments about the likelihood of different tendencies in various groups is an inevitable part of personal as well as business decision-making. For example, advertisers know that men are more likely to watch sporting events than women, and film producers know that women are more likely to watch love stories, and men are more attracted to pornographic films.
Vigilance is needed to make sure that profiling of passengers is not abused, and that it is conducted politely. Yet it is unwise to give in to political correctness, and require all passengers to go through the inconvenience and loss of time involved in extensive airport security checks, when only a very small fraction of passengers pose a terrorist threat.