I've never understood the logic ICBMs. Yes, they are the ultimate long-range weapon. But it there are much easier and cheaper delivery mechanisms than an ICBM. I bet you could pack one heck of a nuke inside a standard shipping container and then have it detonate once it's inside the harbour.
Similarly ABM presumes the existance of ICBMs (which is much less since the fall of the USSR) and the capability to detect and destroy with a high degree of accuracy and precision something which is a very small target for a very short period of time. Easier to hit a whomp-rat while racing the Boonta eve.
Well, ICBMs can be retargeted in a short period of time, so you don't find yourself wanting to destroy Murmansk when your nuke is idling on a Moscow loading dock. ICBMs are not prone to detection by your enemy when they're idle, primarily because your enemy can't get to them, or if he can, he doesn't know where it's going.
Shipping containers take days and paperwork to move about without drawing suspicion, and can't be taken some places (military bases, etc.) which would screen containers and trucks for these sorts of things-- further, you'd need a trained covert agent to detonate the thing, probably at a cost to his or her life. ICBMs deliver 8-10 warheads to the rooftop of your command and control center in less than an hour after being dispatched by a pair of mid-grade enlisted men who get to live through the whole thing. It's hard to see how that's not so overwhelmingly superior to a shipping container that it's barely worth considering.
Furthermore, the "Anytime, anywhere" aspect is a major point of deterrance, the other point being our second-strike capability that we maintained over the north pole for all those years.
Something else worth noting is that all of these missile-shield systems force (and fund!) innovations in the radar detection systems, to say nothing of the systems that must be invented to handle the information of all those targets. Someday that technology will make its way into the private sector-- maybe into the bumper of your car for collision-avoidance or automated driving-- who knows? Perhaps it'll find its way into a meteor-detection system, an automated spacecraft, a missile shield for ships at sea (since guided-missile attack is the primary military threat these days).
You can ship a container from anywhere in the world to the US for $3k. Terrorists don't change targets, have plenty of time, disposable operatives and want contamination not destruction. Less than 1% are screened and if they are detected by port security....detonate.
There are a lot more terrorist threats than missile threats in the world and the countries with missiles are assured of being vaporized.
Just because the new threats are around, it doesn't mean the old threats have vanished. As for what they want, I'd say it's more likely that they want destruction, but are willing to settle for contamination, since it's considerably cheaper and technologically simpler. On the other hand, maybe they could just take over a missile silo or one of those missle-trucks that the USSR had as its second-stike capability.
You're right that a container bomb isn't likely to be screened, and that's a problem. But that does not mean that ICBMs are absolutely logical for those who can afford them.
Finally, it's usually fruitless to insist that money spent someplace in government would better be spent elsewhere, when in reality the government would prefer to just spend on both since it never seems to pit one thing against another, and I don't recall anything being deliberately de-funded in order to pay for something better. Every little program is reviewed on its merits, even if those merits include a well-greased Congressman or a well-briefed president. I've already spoken as to some of the merits of the missile shield research, though I don't know if it includes any politicians.
Personally, I think we could save a ton of money by buying and burying the nuclear materials that we know is out there. I read an interesting (non-fic) book called "One Point Safe," which was the basis of the excellent but panned movie "The Peacemaker." The book was a not-terribly-alarmist discussion of the state of nuclear materials in post-soviet Russia, and did a better job than any other source of convincing me that a padlocked shack full of plutonium cores wasn't terribly secure.
It's not cut one program to fund another neccesarily: but you can put both seperately against our big budget deficit. And also, what's worthwhile for a politician to spend politcal capital on, so to speak...