The Bush administration’s decision to take a shot at a crippled spy satellite Thursday has provoked no shortage of complaints from the disarmament crowd. “The politics are terrible,” grouses Jeffrey G. Lewis of the New America Foundation, in the New York Times. “We will be using a missile defense system to shoot down a satellite.”

Yes, we will. And the politics are terrible only for liberals who are ideologically committed enemies of missile defense. A successful effort to protect people from a man-made device falling from space would counter some of the arguments that missile-defense critics have been repeating since Ted Kennedy started throwing around the term “Star Wars” as an insult.

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The satellite in question failed more than a year ago, soon after its launch. Much of it will burn up as it reenters the atmosphere — but not all of it. The satellite is believed to carry half a ton of hydrazine, a rocket fuel that could prove lethal if it falls on an inhabited region — talk about terrible politics. With its embryonic missile-defense system, limited though it currently is, the U.S. military has the option of trying to do something about that. These are remote probabilities, to be sure, but we have the ability to assuage these risks. Why not take a shot?

The plan calls for an Aegis warship to launch an SM-3 missile at the satellite, probably within the next week or so. A successful strike would guarantee that the hydrazine drops harmlessly into the Pacific Ocean rather than falling as a deadly rain over Fargo or Warsaw.

The operation would also highlight the usefulness of hit-to-kill technology, the guiding principle behind America’s existing missile defenses. The program’s foes always claim that the Pentagon’s tests are contrived. This demonstration surely won’t be. The conditions won’t mimic a surprise attack from North Korea, but they will include unpredictable factors and will possibly involve real-world stakes. Moreover, missile-defense engineers are likely to learn valuable lessons from the experience even if it fails.

This won’t be the first time our country has taken aim at a satellite. In 1985, an F-15 shot down an obsolete scientific probe. Soon after, Congress banned further attempts. China became the first nation since that time to test an anti-satellite weapon when it destroyed an orbiter with a missile. The incident sprayed debris in the flight paths of other satellites and sparked a diplomatic row, but it also served as a kind of wake-up call: Like it or not, we live in an age of space warfare. We can recognize this fact and prepare for it, making sure that our military’s increasingly space-enabled deployments are secure and our homeland is safe, or pretend the problem doesn’t exist until there’s a crisis.

Military officials insist that the Pentagon merely wants to prevent a potential disaster. At the same time, a successful display of missile-defense prowess can serve a supplementary purpose if it reminds potential adversaries that we’ve developed sophisticated anti-ballistic technologies.

Some detractors refuse to accept the Bush administration’s statements at face value. “In the history of the space age, there has not been a single human being who has been harmed by man-made objects falling from space,” complains Michael Krepon of the Henry L. Stimson Center, in the Washington Post. “There has to be another reason behind this.”

Perhaps there is: The spy satellite is believed to carry state-of-the-art imaging equipment — and who knows what else? If it were to fall into the vast wilderness of Siberia, surviving parts might be retrieved by people who shouldn’t have access to them. That’s all the more reason to knock out the satellite on our own terms.

By coincidence, the 25th anniversary of Ronald Reagan’s speech on the Strategic Defense Initiative is almost upon us. When it arrives, on March 23, we’ll know whether the military has managed to shoot down a falling satellite. Let’s hope that this speech soon receives a fitting memorial on the edge of space, when a missile that exists because Reagan called for its creation demonstrates a capability that we need now as much as we did then.