(groan… so much misinformation…)
First, the ABM treaty (which does not have a 25 year duration, it is of unlimited duration) itself does not have anything specifically to do with nuclear weapons. Rather, the fact that national ABM systems are now for the most part prohibited under the treaty, as others have mentioned, allowed the USSR and the US to move on to SALT I (signed just after the ABM treaty), as well as the START treaties of the '90s which have actually reduced the stockpiles of nukes in each country. Build a national ABM system and talks on SALT III will be dead INSTANTLY. Why is that imporant?
Because the SALT treaties (like most others, inc. ABM) allow countries to opt out if “extraordinary events” have jeopardized the supreme interests of the states parties. Since a US violation of the ABM treaty would unquestionably be an “extraordinary event,” Russia would have no further incentive to continue with arms reduction.
Why is that a problem? Because aside from the principle of maintaining parity with Russia, there is no conceivable reason for the US to maintain 2,500 plus strategic nukes… except maybe if that comet starts heading towards earth. Maintaining that huge force has a load of problems associated with it as well. To maintain this stockpile, the US spends somewhere around $4 billion a year… that’s not building new weapons, that’s just making sure the ones we have work.
Furthermore, states would likely start withdrawing from the Comprehensive Test Ban Treaty which is a fantastic idea for several reasons. First, nuke tests are terribly damaging to the environment. Second, there is NO FORESEEABLE CHANCE that the US will need to do full nuclear tests. The US conducts subcritical nuclear tests (where the nuclear material comes very close to explosion, but doesn’t), and the building of the National Ignition Facility virtually eliminates any scientific need for real testing. Testing now is only a political maneuver.
Second, contrary to Danielinthewolvesden’s comment, the treaties signed with the USSR are legally recognized to be binding in our relations with Russia.
Third, I’m sorry to those who think the Patriot worked, but it did not. Similarly, the trials done on theater missile defense have shown that we are nowhere near getting even a 25% reliablilty out of intercepting missiles. And whoever mentioned the interception of anti-ship missiles should know that ballistic missiles travel at about 15,000 mph, as opposed to 600 mph for an anti-ship missile. Not even close to the same thing.
Fourth, the issue isn’t just a national ABM system, but also the potential deployment of TMD systems (which are not prohibited by the ABM treaty). These are two separate issues. However, TMD, if it ever works, will be deployed to Japan, and likely South Korea and Taiwan. Result: China and North Korea get pissed off.
Finally, is there the ability to deal with ballistic missile threats by other means? YES. People talk a lot about “rogue states” and irrational actors which might launch an attack on the US, but if you get down to it, the US has been very capable of dealing with such threats through negotiation. Guess what – if you look into it, the states the US fears as “rogue states” are actually far more rational than they are portrayed, and US policy makers KNOW IT. The example I know best, North Korea, is outwardly portrayed as a maniacal regime capable of anything, but the negotiators dealing with the DPRK understand that they deal in real politik to a degree Kissinger would be pround of. Kim Jong Il may be an odd fellow, but his foreign policy has astoundingly simple logic to it.
Conclusion? ABM is tremendously expensive. It won’t work for at least ten years, if ever. It undermines any hope of continued arms control unless the technology is shared, which I believe ABM proponents would fight tooth and nail against. It violates our treaty obligations. It’s a bad idea.