You missed a pretty obvious (and in my opinion the actual) reason off - to defend against ballistic missiles anyone? How could you possibly miss that one off!?
BMD is aimed at Iran and North Korea, two countries most people on here would agree America wouldn't mind "regime changing". However, they are also two countries that have, or are suspected of wanting, nuclear weapons (in NK's case, they can just about reach the American mainland, altho it'd be a hell of a lucky shot). America cannot invade a country that could wipe out the invading force at the flick of a switch, however, if they can intercept a single, or very small number (which is all NK or Iran would have) then they can invade, and that, imo, is the reason for missile defence