Second strike capability deters full scale nuclear first strikes, but not necessarily limited strikes where the gamble is "they won't destroy the world just bec

Second strike capability deters full scale nuclear first strikes, but not necessarily limited strikes where the gamble is "they won't destroy the world just because we destroyed a city." It also does nothing against accidental launches, or strikes ordered because of miscommunication or irrationality. If we were confident we could deter all strikes, there would be no need for missile defense abroad either - our threat to retaliate would be sufficient. In any scenario where a carrier group is potentially getting nuked we're basically in a full scale nuclear war with a peer adversary. Those other ballistic missile defense systems do serve a purpose, but they are inadequate on their own. They currently exist because they were technically simpler, not because they are superior. The purpose of ballistic missile defense is not to deter a state from attacking with ICBMs, it is to intercept ICBMs. For small strikes such as the scenarios given above, it can defeat or mitigate them. For sufficiently large strikes, nukes will get through, but fewer will get through, and importantly the adversary doesn't know which will get through, so for a given arsenal size they need to either double up on targets or accept a significant fraction of targets not being destroyed, either of which means more stuff is left standing than if there wasn't such a missile defense system in place. Again, defense systems are not meant to be undefeatable, they are just to force your adversary into incurring the cost to potentially defeat them. There is a deterrent effect to any weapon system - if it's harder, riskier, and more expensive to defeat the adversary, all the less reason to try - but that's just an added bonus. The argument that this system encourages development of space based weapons falls on deaf ears. Space based weapons are already under active development by multiple nations, and will be implemented regardless because an adversary's satellite network is already a serious military asset to be attacked and defended. Given the choice between weaponized space and not being nuked versus probably still weaponization of space and being nuked, I know which option I'm choosing. I am even less compelled by the claim that a space based interceptor, whose sole purpose is to prevent nuclear armageddon and has no offensive capability whatsoever, somehow equates to space imperialism. The would be nuclear war mongers seem like the real enemy of free spacefaring nations. There is a very real question of opportunity cost. Developing and deploying such a system is resource intensive, could those resources be better spent elsewhere? Is there a better way to defend against these threats? Are there realistic alternatives that prevent nuclear war by other means? I think a compelling case could be made for either. Whatever that alternative is though needs to be better than "sit around and pray no one launches nukes."