Paul Linebarger touches on this issue in Psychological Warfare, Infantry Journal Press, Washington D.C., 1948:
It would have helped domestic American politics to call the Japanese Emperor a monkey, a swine, a lunatic, a witch-doctor or comparable names; some people did so. But if the American government had done so at home for the purpose of rousing its own public, the Japanese home public would have been roused even more with the net result that the Americans would have lost by such attacks.
The Emperor is mentioned in depth in Office of War Information training lectures. Robert Kinkead spoke of him in a lecture entitled,“Directives and Editorial Control” in a lecture to OWI students in San Francisco in 1944. He said:
There was a tendency in the first days of operation out here on the Pacific to want to refer to Hirohito as a slit-eyed, buck-toothed little son-of-a-gun, or other colorful phrases of that sort, some of them not suitable for the air. And they said, “Why not? He is the head of a country and that country is our enemy. We are fighting them.”
The State Department and many others who knew Japan pretty well said, “It is just about as effective to attack the Emperor of Japan as if the Japanese were to attack George Washington.” The Emperor of Japan is a historic institution to the Japanese and it doesn’t do much good to call him names.
The best way to create disunity in Japan…would be to take advantage of the loyal feeling the Japanese have for their institution of Emperor…to start spreading the idea that the military clique is ruling Japan and has shoved the nation into war by deceiving, misleading and misguiding the Emperor…
Three reasons that America thought it ill-advised to attack the Emperor are mentioned in the book Mirror for Man, Clyde Kluckhorn, McGraw-Hill, NY 1949:
First of all, It was important that the United States explain to the Japanese that the Allies were fighting their military and political leaders, and not the Emperor, who was held in special fascination by the people.
Second, since the Emperor was so beloved and worshipped by the people, to attack him would be counterproductive. It would intensify and prolong the Japanese resistance and give the militarists a rallying cry.
Finally, the only hope that an American victory would lead to the complete surrender of Japanese troops scattered over the Pacific islands and on the continent of Asia was for the Emperor to give the command for them to lay down their arms. This respected leader of the Japanese people must be kept in place so that he can unconditionally surrender his forces and so that there can be a smooth transition of power.
The author adds, “It is always more effective to preserve some continuity in the existing social organization and to work at reorganization from the established base."