"FDR, and others (e.g., Churchill), thought the Japanese had rational leadership which could be deterred."

LOL.
The entire world in the 1930's was a fascist swamp with more and less vicious fascist countries everywhere. Japan's Emperor was pure evil. Japan was one big fascist cult of war  with a racist superiority complex, the aristocrats demanding god-like authority over their subordinates.
   And the Western countries were almost as bad.
    Gays, women, ethnic folks, Jews, indigenous people, Chinese, French-Canadians - all were mistreated as second class citizens at best, jailed as criminals at worst. Life was very nice for middle class white folks, sure. But Canada and the world was a fascist swamp. It was only a matter of time before the alligators, crocs, snakes, and others attacked one another.