[MMMMMM]

The plan is eventually to have a multi-layered missile defense system which, I think, would include some ship-based or sub-based interceptors, as well as land based and space-based interceptors.

China only has around 25 nukes (as of a couple of years ago, maybe still). Whether those include MIRV's I don't know, but if the missiles could be intercepted before re-entry (before multiple warhead split) I don't see why we would have to be able to intercept 500 missiles to be able to nullify or manage a nulear threat from China.

Also consider that our country could absorb one or two nuclear hits far better than many hits. We would eventually recover (painfully and at great cost) if one or two missiles got through, but we might not if a dozen, or a few dozen, got through. So it matters a great deal if we can stop most or all of the missiles a rogue nation or China might launch at us.

MAD was OK during the Cold War, but if unstable regimes or fanatics get nukes and the means to deliver them (say North Korea, or Iran's mullahs), then I wouldn't think we should be placing too much confidence in MAD.

The government of the USSR was run by men who were not fanatical or potentially suicidal. The same can't be said with great confidence about certain other regimes.