Somehow, people have the notion that complex systems should be flawless from the beginning. That almost never happens in the real world. Complex systems are tested in an incremental fashion. Before they tried any actual intercepts, they fired the test missiles to see that they worked. Once they were satisfied, they started actual intercept attempts. Two of the four attempts worked. More tests, each more complex and demanding than the last, will be required before any NMD system could be considered operational. They have not even tested the interceptor vehicle on the planned booster yet. That booster was successfully tested a couple weeks ago. They also have to test the system using the full support of the intended radars and satellites which have not been built. During these tests, more failures are almost certain to happen. That's why we test the system in the first place.

I shutter to think what would've happened if the demand for instant perfection had been the norm in earlier days. Just off the top of my head, I can name several military aircraft that lost their prototypes but went on to successful careers. The XB-17 prototype crashed, as did the B-29, a bunch of early B-26s, the P-38, P-47, and P-51 prototypes. Had we dropped those programs because of early failure, we would've lost some of the most important planes in our arsenal in WWII. Not only that, but failures continued into the jet age. Those early jets built in the 1940s and 1950s suffered many crashes. Risk was considered part of the job back then. Something like 12 of the first 14 F-14s crashed. So did all of the stealth fighter proof of concept (Have Blue) vehicles and some of the early F-117s. The YF-16 prototype was damaged beyond repair and so was the YF-22.

I'm not a big supporter of NMD as a military necessity. However, I do see the value of being able to remove a marginal nuclear power's ability to use nuclear blackmail against us. Suppose if back in 1990 Saddam had even a couple nukes and the means to deliver them, even if only to other Middle Eastern country or to Europe. Would we have opposed him over Kuwait? North Korea tested a missile a couple years ago with the range to hit Alaska or Hawaii. If they moved on South Korea, would we risk Anchorage or Honolulu? Nuclear blackmail could be successfully used to hamstring us when it comes to opposing hostile acts by such countries. That alone may be worth the costs of NMD.