As a former "Missileier" in the Hawk and Nike Hercules systems I think the idea of a national missile defense is comendable. We used to have one, (Nike) albeit obsolete, and it was dismantled in the mid '70s. Air defense is a highly technical problem, that also needs trained and dedicated personel for operation, but then what modern warfare system isn't. The only sure thing is, if there isn't one, there won' be one if it is needed (a Hawk Battery would have been handy on 911).
As for "rogue states" I think missile subs designed for air defense are more practicle than CONUS based air defense units.
What ever we do, the fact is that at this time we have nothing. Let me repeat that, NOTHING.
As a former "Missileier" in the Hawk and Nike Hercules systems . . . That's an item of personal interest, having lived a few blocks away, long ago, from a Nike base on Chicago's lakefront.