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?

True. The perpetrator could be some kid, doing it for lulz.

Edit: As in "WarGames".