It is amazing the controversy that missile defense continues to arouse nearly 30 years after Ronald Reagan gave his famous “Star Wars” speech. Yesterday I posted an item saying that Reagan’s vision of intercepting missiles had been vindicated by the success that Israel’s Iron Dome system is having in knocking down Hamas rockets–some 300 so far. This sparked much indignation on Twitter and the blogosphere, with a graduate student named Matt Fay writing an entire blog item in reply arguing “Iron Dome Does Not Vindicate SDI,” and political scientist/blogger Robert Farley posting numerous tweets in a similar vein. They attack me for one alleged factual error and for a larger conceptual error of equating defense against Russian ICBMs, which have a range of thousands of miles, with defense against short-range Hamas rockets which can travel no more than 50 miles and often less. Let me explain in brief why I stand by my original point.

First, the supposed factual error is more an omission than a mistake. I wrote that “the U.S. West Coast is actually protected by a limited ballistic-missile defense system based primarily around satellites, sea-based Aegis and X-band radars, and Standard Missile-3 interceptors.” Fay points out I neglected to mention the ground-based interceptors located in Alaska and California. Fair enough; I should have mentioned them. But the first line of defense against missiles aimed at the U.S. remains warships equipped with Aegis radar and Standard Missile 3′s–as a quick glance at the website of the US Missile Defense Agency will confirm. In the future a new generation of SM-3′s will also be based ashore in the U.S. If North Korea were to launch a missile our way, an Aegis-equipped Navy ship would be more likely to shoot it down than one of the ground-based interceptors in the continental U.S. But they are all part of a larger system with redundancy built in to increase the chances of a successful interception.

What about my supposed error in equating rocket defense with missile defense? Granted there are major differences between the two–missiles travel farther and faster and they can have multiple warheads and various defenses against interception. But the fact that missiles take time to prepare for launch, that they have to come from launching platforms easily observable from the air, and that they are often in flight for many minutes–roughly half an hour to get from Russia to the U.S.–actually improves the chances of interception. By contrast Qassam rockets can be set up with no notice and detonate 30 seconds after launch. The fact that the Iron Dome system has been 90 percent successful, if initial reports are to be believed, is actually quite impressive and does vindicate Reagan’s much-mocked vision of using one projectile to intercept another.

Some critics point out that even a 90-percent success rate for national missile defense wouldn’t do much good, because letting even one nuclear-tipped missile through could be devastating. True enough, but, Reagan’s sometimes grandiose rhetoric aside about “eliminating the threat posed by strategic nuclear missiles,” even markedly reducing that threat would be of great benefit. In the days of the Cold War, the Soviets plotted to launch a devastating first strike on the U.S. But if a defense system had knocked down many of their attacking missiles, that would have preserved America’s ability to launch an even more devastating counter-strike. Thus if missile defense had been in place in those days it could have improved deterrence and reduced the risk of a nuclear attack. Today missile defense can achieve more limited, but just as valuable, objectives by preventing North Korea, Iran and other rogue states from threatening their neighbors and their neighbors’ ally, the United States.

I remain puzzled by the emotional response generated by any advocacy of missile defense. Why do so many critics have such an investment in trying to prove that missile defense doesn’t work? Isn’t a good defense the best way to keep the peace?