The World Trade Center attack may prove to be one of the grimmest moments in modern American history. Understandably, most Americans are enraged and demand revenge, while despair and fear are evident even in people who, only a very short time ago, managed to maintain a fairly detached view of the political scene. In this atmosphere, very few are prepared to complain about the strict new security precautions that are being imposed at airports and public facilities. Quite apart from the grief they feel for the victims of terrorism, citizens who would normally be sensitive to government encroachments on civil liberties believe that rights have to be yielded in order to secure better protection.

In theory, this idea of a tradeoff is not unreasonable; in practice, the notion is poorly founded. When rights are eroded in the heat of war and terrorism, these changes rarely produce any practical benefit beyond a general sense of communal sacrifice. And once they are gone, these rights and liberties are very, very difficult to regain. To take an obvious example of a futile expansion of official powers: Just what has been gained by the massive extension of identity cheeks at airports and the requirement that travelers carry official identity cards? Anybody who believes that such controls will prevent terrorism is obviously deluded: As eery antiterrorism professional knows, the first requirement for a serious terrorist is the ability to procure immaculate false papers.

In the age of the internet, many of the critical struggles for rights necessarily occur on the electronic frontier; here, too, terrorist outrages provide a convenient excuse to encroach on individual rights. Over the last two years, privacy battles have raged over a proposed FBI system called Carnivore, designed to intercept potentially vast numbers of e-mails in search of suspect communications dealing with (for instance) terrorism, drug trafficking, or child pornography. Court warrants would not, of course, play any role in this process. Carnivore was fiercely opposed by a broad cross-section of activists, including political conservatives and economic liberals, in addition to the traditional civil-liberties constituency.

The whole idea of e-mail snooping has been desperately controversial, and it took a bold bureaucrat to defend it—at least, until the fall of the World Trade Center. Suddenly, massive e-mail snooping became the norm, Carnivore surveillance became widespread, and nothing more has been heard about the need for warrants. The logic is simple: Would any internet service provider like it to be known that it had delayed or obstructed the FBI in a quest for information that might have prevented more airliners from being hijacked, more buildings from being blown up? The question is absurd: Carnivore is here to stay.

But this is not simply a conflict between effective policing and civil-libertarian idealism, between good cops and naive eggheads. If the FBI or any other agency has any reasonable suspicion that intercepting communications might help suppress terrorism, I wish it success in its endeavors. The problem is that, in most instances, this is just not going to happen, and random trawls can even do more harm than good. Basically, too much information can overwhelm a system, even if the individual pieces of information are priceless.

The principle can be illustrated from any antiterrorist or counter subversion war, from Vietnam to Algeria to Ulster. Time and again, security forces have tried lo pull in hundreds or even thousands of suspects, who are either not interrogated thoroughly, or who produce so much information that the system is swamped. Far better to round up a dozen or so activists who can be interrogated in depth, with the information properly analyzed and assimilated. Those wars, of course, are ancient history: They occurred in the dear, dead past, before electronic surveillance became so miraculously “effective,” and computers could (in theory) analyze all the data. Even so, somewhere along the line, inefficient human beings have to read and react to what the computers are collecting. And they are going lo miss a great deal.

Carnivore, in short, might be the worst of both worlds. Random snooping interferes massively with the privacy of communications, while offering little chance that bad guys will be apprehended. Furthermore, Carnivore is a symptom of America’s over reliance on electronic technologies, which have largely displaced traditional human intelligence tactics—the use of spies, moles, and defectors. These methods have worked well in the past, and properly applied, they might even have averted the catastrophe in New York City this past September.