I don't think a missile defense systems will be able to work in the next 20-30 years. We don't have anywhere near the technology and the defensive maneuvers that a multiple missile warhead and fake missiles will be impossible for the technology we are developing. I will cost them much less to defeat the system. But it will keep many of our military industrial complex employed with a boondoggle.
Plus MIT has now started to investigate their own test results which they think were fabricated to support all their previous results that our government has used to proceed.