Plus, what if multiple state actors penetrate a system and each lay their own "implants"? Mutually assuredly destruction only works if you can attribute an attack. Unless you're planning on destroying non-guilty actors too. What if NK, China, and Russia all hack the same system and then eventually the system fails catastrophically as a result of malware and no one takes credit. How could the US respond? What if the perpetrator were an adversary that wasn't even known to have penetrated the system?