You realize that no current missile defence system could hold back a saturated ballistic missile strike, right?
I know and I hope this situation won't change during my lifetime (and over), it's exactly why I am against space weapons: they imperil MAD. I remember that few years ago on People's daily there were several articles stating China favoured a ban on space weapons, few monhs ago on the same e-journal a PLA general affirmed that PLA must play role in space, and recently US unveiled their space bird. My impression and conclusion is that weaponization of space is slowly beginning. ICBM of course will stay as the main end-of-the-world weapons for several decades in the future.