History

This is how I remember his series on the Japanese involvement in WWII:

Carlin talked about the Japanese military leaving gruesome "messages" (through terribly mutilated corpses of American soldier) to Americans, which in turn led Americans to take fewer POWs and also ramp up the violence. Additionally, this led to fewer Americans units who may have otherwise surrendered as POWs to continue fighting even if it meant they would all die; they were terrified to be captured. The Japanese military also knew what effect this must have on the Americans, and as a result would refuse to surrender in fear of similar treatment / reprisal.

Japanese soldiers would report this back home to their families. Combined with the propaganda civilians received from their government and the stories from the front, many people believed that when the Americans landed in Japan, that the soldiers would eat their children. It was because of this sentiment it was believed that the Japanese populace would never surrender, and the fighting on the Japanese islands would require killing far more people as the invasion progressed northward.

It is to be noted I am not a historian, and I'm just someone who listened to a really long podcast a couple years ago. He's more of an "historian" than I am, and he seemed pretty credible to me. I have done no other reading or research on the topic, and I probably shouldn't have commented here to begin with.