So, pray tell, what would you have done in the US' position?

This is an incredibly useless question. Any socialist would tell you "let Japan's former territories decide what to do" barring the mainland, which would require occupation for a period to purge the fascists (something the US deliberately neglected to do). There would subsequently be one China, one Korea, and I don't know whether Japan's referendums would result in independence for Okinawa or Hokkaido (I doubt it, but idk), but either way the main body would not be one that pays annual tribute to some of the most heinous war criminals in history.