Why would someone deny the horrors of the Japanese?
Say better, why are denial and revanchism so rare among Germans? It's very common for people to idolize their ancestors at the expense of other peoples', it's difficult to accept that your ancestors did monstrous things.
Look at the number of Confederate flags and the widespread denial that the Civil War was about slavery in the American South. Or the number of Russians who idolize Stalin. People like a good nationalist ideology that reinforces their own sense of greatness, and unless it is THOROUGHLY discredited, lots of them will stick with it even if everyone else realizes how horrible it actually is.
What Japan needed, I think, was for its homegrown brand of fascism,
Taisei Yokusankai, and its predecessors, to be demonized as thoroughly as Nazism was postwar. Japan's militarism was built up during the 20s-30s and had about as much in common with traditional Japanese culture as Nazism did with traditional German culture or Fascism with Italian culture (i.e. a rather warped version) - it could have been more thoroughly discredited than it was OTL. I'm not entirely certain how or what would be necessary to accomplish this, however.
