A lot of people have said that the missile defense shield is impossible. It can't work; it won't work. And I tend to agree, here. There are simply too many factors. Decoys can be too good and are relatively cheap, so that even if the acquisition and disabling of a target were possible using today's technology, deciding what is a decoy and what isn't raises the bar to a level that can't be obtained. What is possible to discern? Reflectivity, heat, speed? And can we simulate these well enough to make effective decoys? Right now, the technology for duping a missile defense shield is far beyond the technology for even locking on and hitting any target--decoy or not. And practical decoys are simple and cheap. Re the shield: Impossible might be too strong a word. Improbable is better.
Still, people for greater defense spending and the missile defense system wonder why we're so cynical about a good idea(l). A Republican might ask, "When did it become impossible for us to build a missile defense shield?" The answer is: shortly after it became impossible for us to slow deforestation, stop man-made extinctions, reduce poverty, fix public education, and tap alternative sources of power. We've been told that these are all impossibilties for years by the very same people that are now saying Missile Defense is right around the corner and we should be optimistic about its future. Well, thanks, but no thanks.