No missile defense, even the best hypothetical one, is perfect. No sane politician would provoke an ICBM attack from a nation so armed, defense or no defense. And if the defense, as stipulated, is much less than perfect, this is even more insane. If you have such a person running the country, the missile defense or lack thereof is the least of your problems.

But that is exactly what the neo-conservative ABM boosters have been saying: we need ABM because we might be afraid to get into wars with nuclear-armed countries otherwise.

Their real concern has not been that North Korea would lob a missile at us for some reason, and we wouldn't be able to stop it. Their fear has been that we would be afraid to invade a N. Korea that has ICBMs and conduct "regime change", or that we wouldn't be willing to go to war with China over Taiwan, due to China's ICBM capability. With missile defense, they believe it is much more likely that a president would commit the nation to those poliices, even though they risk an ICBM being lobbed at us (if North Korea had nukes, and we were intent on occupying the country and destroying the regime, they'd have little incentive _not_ to launch, after all).

One possibility is that these hawks believe that missile defense will be so close to perfect that there isn't much risk in these scenarios. In which case, it really does matter a LOT if missile defense doesn't work as well as they think, since they are inclined to pursue policies that only make sense if the system is extremely effective. If their strategy requires that ABM systems be damn good, then I sure hope we test those systems enough to verify that!

The other possibility for the neocons is that, contrary to your claim that only madmen would do so, they really are willing to pursue policies that run a significant likelihood of a nuclear warhead being detonated on an American city.

In the case of Perle, it was clear where he stood: he was willing to run the risk. It was pretty clear in that interview I mention that Perle thought the important thing was that a president believe the ABM system would work, and act as if an impenetrable shield was protecting America, even if the system would not actually stop any missiles.

In other words, missile defense is worth building if it fools presidents and fools the public into thinking that the US can act with impunity against nuclear-armed adversaries. Like convincing a reluctant (but dumb) soldier to charge a machine gun nest by telling him you've given him a magic helmet that stops bullets.

If I were certain that missile defense was seen as an extra layer of safety, just a defensive measure against accidents, rogue launches, or acts of craziness, I could support it, and could agree that even leaky defenses would have some purpose. But core missile defense supporters among the Republican national security elite have wanted it not as wall around our keep, but as a shield to hold in front of us as we advance -- something designed to counter the reluctance of modern politicans and citizens to engage in costly wars. Aimed as much at installing false courage on the home front as at having any actual military effect.