Compartmentalizing and Japan's Attack on Pearl Harbor

One of many things that struck me during Dr. Yamashita's lecture was that the architects of the Pearl Harbor attacks had been educated and spent a great deal of time in the United States. This was incrediby surprising to me, as I would assume (you know what they say about assuming things...), that once you had spent time with a group of people, it would humanize them as a group, and to go back and design an attack meant to destroy and kill would be morally impossible. It is always easier to hate and demonize a group that you have never had personal contact with. This makes me wonder if this is just part of the compartmentalization that many military personnel do on a regular basis, or was their experience in the States so distasteful or negative that they had no problems attacking the country where they received a portion of their education?