alt Hacker NewsThat worked in 1970 because there were exactly two players who had incentive to not spend all the money so they agreed to reduce the total ICBMs instead. In the current world there are too many actors - it won't work, they can make thousands of missles. Ukraine has already proven you don't get to control when you are attacked. Thus the only option today is cost reduce defense and produce enough to intercept several thousand per day.
It doesn't matter if it's the only option if it's not possible to do it.
Maybe it is possible. It does seem like it may be possible to defend against cheap drones with cheaper systems. Use lasers or good old-fashioned projectile guns instead of interceptor missiles.
For defending against proper missiles, I don't see how it's possible with any near-future tech. Guns and lasers don't work. You have to use a missile and it's going to have a cost similar to the cost of what you're shooting down. Peer enemies will be able to out-build you and many missiles will get through your defenses.
Shooting some down is better than shooting none down, but your enemy won't ignore your defensive systems. Shooting down 1,000 and having 1,000 get through is not better than shooting down 0 and having 1,000 get through. If building defenses just provokes the other side to build more offense, it's not worth it. If they're going to build the same amount of offense either way, then it might make sense to build up defenses.
Here's something to consider. The US has interceptors capable of shooting down ICBMs and with enough range to protect the whole continental US. There are currently 44 such interceptors. They cost about $75 million each. Standard procedure is to shoot four interceptors at an incoming missile to increase the likelihood of a kill, so that's about $300 million per incoming missile you want to counter. That's very much worth the cost if it prevents a nuclear warhead from reaching its target.
Russia and China together have maybe 700 ICBMs if we take a high estimate. For $210 billion, we could have enough interceptors to shoot down almost all of them. Round it up to $300 billion to account for all the infrastructure they'd need. That's a bargain compared to saving hundreds of American cities. So the question is: should we do it? So far, the American government has said "no." I agree with them, despite it being a bargain. Do you?