Wow, that’s an unusual alternative history you have there. I don’t think you’d be able to find much evidence to back it up.
While their ability to attack the American mainland was limited, their invasions of China (which aided the rise of communism), Korea, Taiwan, Indonesia, the Philippines, and so forth, makes the idea they were “no threat” sound a little absurd on the whole.
Some historians and governments hold Japanese military forces, namely the Imperial Japanese Army, the Imperial Japanese Navy, and the Imperial Japanese family, especially under Emperor Hirohito, responsible for the deaths of millions, some estimate between 3 and 14 million civilians and prisoners of war through massacre, human experimentation, starvation, and forced labor that was either directly perpetrated or condoned by the Japanese military and government. - Wikipedia
Shits and giggles indeed.