Quite correct that only overwhelming force would cause Japan to capitulate.
Barbarism was encouraged. They were already taking Chinese civilians & using them for bayonet practice and using healthy Chinese as surgical guinea pigs for inexperienced military doctors. They were inculcated in brutality and taught to believe they were a favored race (believing that the Emperor was actually a living god) and that everyone else was sub-human. This mindset made their culture increasingly barbarous and impenetrable to rational thought or humane appeal. Their belief in their own superiority & all other people's inferiority made it impossible to halt their aggression diplomatically. Two A-Bombs and Stalin's Red Army
poised against them was what it took to force surrender.
The parallels with today's Militant Islam should be obvious.
m2