The Japanese deserved what they got., page-72

"America's exoneration of Hirohito for the countless tens of millions of people slaughtered in his name is without precedent in modern history and has never been explained - not that 'chosen ones' are ever held to account!"

Lappy my take from what I've learned is this.

After the war in the Pacific finished and Japan and its citizens were totally pulverised and nuked, a realistic decision was made by the Truman Administration thus.
The Japanese people needed some focus to recover and become a truly successful human, industrious and economic power.
Removing the Emperor would have totally demoralised the whole fabric of Japanese society.
We cannot just assume that the Asian races will meekly follow the Anglo Saxon dictates.

Leaving the Emperor as this point of focus was a masterful stroke.

You can see how successful this move was by the Japanese recovery and results over the last 50 years.