I think the assumption is that the difficulty of long-range space travel is such that only the "nation-state actors" in this analogy are likely to attack you in

I think the assumption is that the difficulty of long-range space travel is such that only the "nation-state actors" in this analogy are likely to attack you in the first place. Just by existing in a universe with the laws of physics ours has, you're effectively secure against attack from low-tech civilizations.