To the contemporary observer, the 9/11 attacks are significant because they reveal the methods and goals of the followers of a radical strain of Islam. Public debate has focused on the proper response to al Qaeda, its affiliates, and those inspired by its ideology. Legal reform has, to a great extent, also focused on the particular challenges posed by al Qaeda, reflected most notably in the 2002 Authorization for Use of Military Force, which identifies al Qaeda as the enemy against which military force may be directed. David Cole’s proposal fits this approach. He believes that preventive detention may be justified for this particular conflict, and he defends a scheme limited to those involved in the fighting.

But future historians will see 9/11 differently. The terrorist attacks did not actually tell us much new about radical Islam. The significance of the attacks lay in what they revealed about the offensive capabilities of modern technology in the hands of criminals and enemies. Although the 9/11 attacks themselves used decades-old technology, the anthrax attack that immediately followed them and revelations of al Qaeda’s interest in nuclear, biological, and chemical weapons, drove home the point that governments had fallen behind in the race between offensive and defensive technology.

As highly destructive weapons become cheaper, smaller, and more transportable, they pose a greater risk to the lives of innocent people. Not only terrorist organizations like al Qaeda, but also states and ordinary criminal gangs can exploit these advances in weapons technology. Meanwhile, governments and private firms strive to develop defensive technologies that adequately counter the new weapons. These technological developments have produced improved surveillance techniques, screening machines, encryption and decryption devices, drones and other robot craft, vaccines, data mining algorithms, hazardous substance detectors, and much else. Unfortunately, technology still favors offense over defense, putting civilians at greater risk from small groups than at any time in recent memory.

The difference between the general problem posed by the offensive capabilities of modern technology and the particular problem posed by al Qaeda was not lost on the U.S. government after 9/11. The executive branch sought broad powers to address any terrorist threat, not just al Qaeda, and it has exploited the search and surveillance powers obtained in the Patriot Act and later legislation against many actors.

Inherent in the functioning of these powers is a degree of restriction of civil liberties. Critics see the restrictions as excessive, but the rationale for Bush administration’s approach is straightforward. The standard package of civil liberties in the United States—including the right to a trial and other elements of criminal procedure and protections against surveillance and searches—makes sense in a society in which the police can provide adequate protection from criminal threats. But, to an extent that is rarely appreciated, this legal regime is contingent on a balance of offensive and defensive technologies. 9/11 made clear that the balance has shifted.

Once we understand that the civil liberties a society enjoys reflect a tradeoff between security (including protection from criminality as well as external military threats) and the benefits of freedom, and, further, that security at any point will reflect technological changes that are largely outside of that society’s control, we ought to appreciate the Bush administration’s impulse to restrict civil liberties after 9/11. The problem to which the Bush administration and Congress responded with laws like the Patriot Act was not so much the threat of al Qaeda itself, but the vulnerability of the United States to destructive weapons in the hands of anyone with hostile intent.

Cole’s proposal to expand powers of preventive detention against members of al Qaeda, while reasonable within the narrow scope of his agenda, fails to come to terms with the overall problem that 9/11 demands we recognize. What is to be done when the executive branch learns of an organization or even individual who it suspects has obtained, or is likely to obtain, weapons of mass destruction, but can’t convict of a crime? The executive can’t very well ask Congress to declare war against every new shadowy, but potentially harmless, institution or individual who briefly emerges into the light. And yet the implication of Cole’s approach is exactly that: no preventive detention regime to address a new threat until congressional authorization has been obtained.

I suspect that in the next years, even under a more liberal administration, Bush-era restrictions on civil liberties will be retained, at least to some extent. And they will be extended if new attacks occur. It is only a matter of time before a general preventive detention system, not limited to members of al Qaeda and associated groups, will be added to the criminal justice repertoire.

Cole’s preference for a preventive detention scheme that lurches into operation only after Congress declares war on a particular group rests on worries about executive overreaching. This approach, though well-grounded in history, is in tension with rule-of-law ideals, which promote generally applicable laws rather than laws retroactively aimed at particular individuals or groups. Under Cole’s approach, Congress will have to respond to new threats by declaring war against more and more groups and associations until Cole’s limited preventive detention scheme has general applicability. Indeed, it seems likely that, even in the absence of further declarations of war, courts would be willing to apply Cole’s scheme to any dangerous organization with a connection to radical Muslims, with al Qaeda playing just a symbolic role. Secular terrorists, and terrorists associated with other religions, would get a pass for the time being.

A general preventive detention law puts everyone on notice that certain activities will raise suspicions of criminal or military dangerousness, and would thus be more consistent with the rule-of-law values that Cole seeks to uphold.