We let North Korea develop missiles (not that I think they'd be stupid enough to fire them at the U.S. itself), and we build a system to intercept the missiles that just doesn't work: Fledgling US missile shield largely unproven.
It's been years, and they've only had 5/8 success rate? That doesn't count the number of times they had to scrub the tests. And they don't point out how easy the tests probably were set up to be.
Just a waste of money. Talk is a hell of a lot cheaper, and would probably work better.