At this point in time, trusting the ABM system to provide protection after a first strike would be suicide, because it is just nowhere near reliable enough.
Russia has ABM too, the 'Galosh' system around Moscow. It works, because it uses a tactical nuke detonated in the upper atmosphere to destroy inbounds. It doesn't have to intercept accurately. It's pragmatic, better to have a small nuke detonate high in the atmosphere, than a big one at ground level.
It's not about the US nuking russia or china for no reason and hoping to survive, it's about making Russian and China scared that the US might do it so they will not be tempted to be militarily aggressive in their regions. And why do you say the moscow defense works, are you aware of test results and failure rates? If the US ABM works 2 out of 3 times, but the Moscow defense net works 1 out 150, or if Russia has openings in its early warning system that can be exploited to knock it out because it requires a centralized, possibly decapitated in a first strike authority or some other factor, then you couldn't say that theirs works or that ours is relatively a failure. I think US intelligence is of the opinion that Moscow's defenses are on the whole so underfunded and under-maintained that nothing high tech can be relied upon to work, and in the future this will be to the point that it's a non-factor in international affairs, and that China's never were any good and will probably not improve. High tech things like missiles have a finite unmaintained life span, and after a certain point you can for certain say none of it will work, and an ABM could be because of quantum luck of one missile working or whatever. I'm not a missile expert and neither are you probably, so you must admit this is possible and seems to fit the facts a little. I always thought the ABM was for Iran and suicide-enemies that have almost no missiles that may launch an unpreventable strike just to get to heaven, but the first strike thing looks plausible after reading that link.
The US system requires a very accurate intercept, which is proving a very hard task. If even one Nuke got through it would be a disaster. 9/11 showed us what panic and disarray can be caused by the destruction of a few buildings in a built up area, a Nuke landing could never be considered victory, even if the opposition cannot launch more.
If was a hypothetical discussion in that link anyway, the US aren't likely to launch a pre-emptive strike against China or Russia, and if they did, I think the International community, previous allies, might have something to say about that.
Oh, I think we all know they'd have something to say about it, do they ever not have something to say..but I digress. When you have a sucessful technological society, technology seeds technology, causing each generation to be exponentially or orders of magnitudes better in every regard than the previous, etc, other countries won't benefit because their lack of money insures that their tech-ability and know-how will be drastrically reduced eventually and ours will be drastically superior, not today, but eventually, maybe 10 years from now I would say. ABM could be developed to the point that nothing could get through, and decoy detetion science improved until decoys would be the maginot line, if the technology keeps seeding better technology while we keep pouring in funding while everybody else has to abandon advancement and probably even maintainance of out-dated and potentially useless against future US tech, missile tech one day. Most people wouldn't want to believe this right now, but I believe it does fit the situation well, and that can't be denied, whether the future will absolutely go down that road might be hard to tell for people like us, but it's a possibility we should acknowledge, and one the US govt would aim for as well.
On a related note, I wonder why the US doesn't implement something like the Russian shield, but instead of high-altitude detonations, why not detonate nukes in space next to the incoming warheads? They must not be in space long enough, or could easily be changed to fly thru the atmosphere more, anyone know? It would be safe and give us the option of surviving an unlikely though possible massive first strike by Russia if it could work..probably not useful for some reason though..