The missile defence system is an enormous waste of money. Whilst it might have some chance of working (unlike the SDI program of the 1980s), the system is likely to have quite a low kill probability - not much good when you're talking of nuclear, biological or chemical weapons. As far as Iran is concerned, the real issue is whether the US can stop the Iranians getting a nuclear weapon before Israel decides they can't take the risk any longer and launch their own strike on Iran's nuclear facilities. At a time of economic crisis, it seems silly to spend so much on a missile system that might never be used and might not work if it is used. The money would be better spent on bulking up the forces in Afghanistan if that conflict is not to drag on for 15 - 20 years.