The United States has a long and laudable tradition of using its technological superiority to improve the moral character of the means it uses for national defense. This tradition could be reversed, however, by a provision in the Senate immigration reform bill that authorizes the construction of a virtual -- rather than an actual -- fence along the U.S.-Mexico border.

An actual fence running the entire length of the U.S.-Mexico border would not only protect would-be illegal immigrants from unnecessary harm, but would also protect the Border Patrolmen whose job it is to secure our frontier. A virtual fence, by contrast, might protect skittish senators from the ill-considered criticism of the liberal media and liberal interest groups, but it would also perpetuate unnecessary risks for illegal border-crossers and Border Patrolmen alike.

Discrimination, which means targeting only things that are threatening, and proportionality, which means using only as much force as necessary to neutralize a threat, are the key principles in weighing the morality of any tactic used in national defense.

For this reason, striking legitimate urban military targets with cruise missiles, as we did in the opening of the Iraq war, is superior to dropping gravity bombs on urban targets, as we did during World War II, because cruise missiles are both more discriminating and more proportionate than gravity bombs. Cruise missiles are also superior, where they can be used, because they can be fired from offshore, exposing our personnel to less risk than planes that must be flown over enemy territory and into enemy defenses.

These principles of discrimination and proportionality -- which are designed to protect human life -- also apply to defending our border. Yet, the Senate's "virtual fence" would use technology to perversely limit, rather than increase, the discrimination and proportionality of border defenses.

A virtual border fence is morally backward.

The actual language of the Senate bill, which is technically an amendment sponsored by Senate Judiciary Chairman Arlen Specter, the Republican from Pennsylvania, authorizes the secretary of homeland security to "procure additional unmanned aerial vehicles, cameras, poles, sensors, and other technologies necessary to achieve operational control of the international borders of the United States and to establish a security perimeter known as a 'virtual fence' along such international borders to provide a barrier to illegal immigration."

Of course, unmanned aerial vehicles, cameras, poles and sensors cannot bar illegal immigrants from entering U.S. territory. They may be able to fly over, videotape, inanimately stand by or passively sense illegal immigrants, but they cannot stop them.

Even if every U.S. Border Patrolman were equipped with a Jack Bauer-type handheld video receiver that pointed out for him in real time the "virtual" image of every illegal intruder attempting to cross his sector of border, it would still be up to the Patrolman to physically stop those intruders.

In the real world, some of those intruders would be bad people capable of inflicting real harm.

A virtual fence is specifically designed to force hands-on confrontations between Border Patrolmen and foreign nationals crossing our border. It would cause dangerous situations, where a real fence could deter and prevent them. Continued...