Kinda shitty to hold that legacy over the heads of an entire people. You're not really making a good case for your supposed moral superiority.
A generation on average is around 25 years. I'm pretty sure the Nanking massacre happened a bit longer than that.
Without invoking war crimes, one could ask about gender inequality, LGBT rights, or the status of racial minorites in Japan. Are these reflective of a particularly "strong culture of morality"?
It's about losing wallets...
I remember the following punch line from one of Japan's anime :).
"To protect the world, we must accept our sins and our accompanying ruin."