The introduction of MIRV led to a major change in the strategic balance. Previously, with one warhead per missile, it was conceivable that one could build a defense that used missiles to attack individual warheads. Any increase in missile fleet by the enemy could be countered by a similar increase in interceptors. With MIRV, a single new enemy missile meant that multiple interceptors would have to be built, meaning that it was much less expensive to increase the attack than the defense. This cost-exchange ratio was so heavily biased towards the attacker that the concept of mutual assured destruction became the leading concept in strategic planning and ABM systems were severely limited in the 1972 Anti-Ballistic Missile Treaty in order to avoid a massive arms race.
Some threats can't be countered, only controlled. And the country that first invented nuclear weapons seems to be in a position to help control its proliferation.
Because you can use dummy warheads, chaff, and other means to lower the efficacy of the interceptor, and you only need a small percentage of your payload to make it through. The defense meanwhile, must be perfect. Missile defense using interceptor vehicles is a pipe dream, pure and simple, and has been for decades even in principle. You can have what appears to be hundreds of warheads falling at once, or even thousands if you’re the US or Russia. Nothing is stopping that well enough to avert mass casualties.
Besides, those interceptors are not cheap, they’re cutting edge while MIRV’ed warheads with dummies are old, proven tech. A live nuclear warhead is only expensive because of the physics package, so a convincing dummy is dirt cheap to make and deploy compared to an interceptor. It’s a losing proposition, and an extension of the truism that armor piercing tech inevitably beats armor in arms races.
The introduction of MIRV led to a major change in the strategic balance. Previously, with one warhead per missile, it was conceivable that one could build a defense that used missiles to attack individual warheads. Any increase in missile fleet by the enemy could be countered by a similar increase in interceptors. With MIRV, a single new enemy missile meant that multiple interceptors would have to be built, meaning that it was much less expensive to increase the attack than the defense. This cost-exchange ratio was so heavily biased towards the attacker that the concept of mutual assured destruction became the leading concept in strategic planning and ABM systems were severely limited in the 1972 Anti-Ballistic Missile Treaty in order to avoid a massive arms race.
Some threats can't be countered, only controlled. And the country that first invented nuclear weapons seems to be in a position to help control its proliferation.