The point of my objecting to your granulation is not that you can’t subdivide parts, but that those subdivided parts remain part of a whole. The claim about natural boundaries within people is irrelevant here in the subject of moral responsibility because the very concept hinges upon distinguishing that which is inside and that which is outside. Those inner boundaries all share one aspect, and that is the very fact that they are, even in your argument, inner, and therefor distinct from outer boundaries. 

Inner/outer is being used for convenience, not revealing something.  

I like this metaphor as well, as it accurately fits the concept of every person a nation unto themselves. :P

It’s not such a bad metaphor, since it exposes the problem with your way of thinking.

People treat subnational units as relevant in international politics quite frequently, which is part of why, while destroying much of the German army during WWII, the result following the war did not involve putting all the Germans to death.  The national responsibility for the war was actually split up according what the individual people and factions within the country did.  In fact, they didn’t even execute the entire German army itself.

Attempting to subjugate a country and knock out its entire army is typically done not because the nation as a whole is sufficiently unified in order to justify total moral liability to all of its subcomponents, but because trying to individually negotiate with all the soldiers and so on while the state apparatus is in the control of a dictator is extremely difficult and unlikely to succeed.

While people may recognize that, say, Texas does not get to speak independently on the international stage, they recognize that it still has an influence on the government which is different from that of, say, Ohio.  This is actually a big part of the large, televised anti-Trump protests, establishing non-total-liability to outside observers.

I could also discuss the nation as a whole as having an inner and outer, and claim that morality exists at the level of the nation and not at the level of the individual.  What makes that boundary more special to the point that we can’t care about the subcomponents?