The Chinese more or less walk into our nuclear research labs, take what they will and leave...and we're worried about setting up a country-wide missle defense system? It's security in the wrong spot, methinks.
The attacks this system is designed to prevent are single threats fired from rogue nations, right? As someone already pointed out, rogue nations aren't likely to be able to hit us with any ballistic missiles for quite some time, if ever.
If a country like China wants to wage nuclear war, we're screwed (and so are they). If they want to set off a nuclear explosion on US soil in the name of terrorism, they'll do it buy smuggling in a small device. A missle shield will not stop a ground threat.
Anyway, the government should just hire M$'s PR firm. Have 'em spin it like this "we already have a defense system, it works great and it's already paid for!". Then the sense of security gets out there and no money is wasted (except to pay off M$'s PR dudes...hmmm that could get expensive).
I stop now due to rambling...