Boost-phase defense does not eliminate all vulnerabilities, especially if it's brought on line ahead of a midcourse layer. Since the kill mechanism destroys the booster, not necessarily the payload, the warhead may continue intact but fall short of the intended target. While there is a good chance it would fall into the ocean, it could fall on friendly territory. But with North Korean missiles initially capable of reaching Alaska, Hawaii and then California, the Pacific mitigates this vulnerability. There is no silver bullet to defend against ballistic missile attack.
Effective defense requires multiple, largely independent intercept opportunities.
As the administration reviews its NMD options, boost-phase defense should figure prominently. Over the long term, it could provide a key layer in a robust defense with capability against most countermeasures. Search the archives of the Los Angeles Times for similar stories. You will not be charged to look for stories, only to retrieve one.