Sadly I learned of that fact during an X-Files storyline in1995. Those of you who think the X-Files was merely about alien abductions would do well know that I think Chris Carter had a braver and more frightening storyline in mind that would have been bolder.
Throughout Season 3 he argued that the alien abduction conspiracy Mulder had spent his life following was a lie. In fact the real conspiracy was based on the reallife American decision to grant amnesty to German scientists in opeartaion Paper Clip in order to win the Space race. Both made that same argument that we did to the Japanese.
Perhaps the most frightening thing the X-Files ever showed was the equivalent of a concentration camp on American soil with American miltary cold-blooded executing a camp full of individual's suffering from Hansen's Disease and leaving them to die in a ditch. The show actually argued that Scully was the subject of those experiments, had been left for dead after they were done, had her ovaries superradiated out of here and was giving a cancer that should have killed her.
I mention this because not long after this Chris Carter introduced the idea of the black oil and basically made it clear the conspiracy was about aliens after all. (The mythology stopped making sense after this but that's a different story.) I don't entire blame Carter for that decision; it's somehow comforting to believe in the idea of alien invasions then the idea that are government is abducting its own citizens, experimenting on them for the purpose of what amounting to chemical warfare and building a superior military soldier. These days, of course, we are very aware of the kind of things our government is capable of doing to its own civilians without explanation - well before September 11th. And for a show that was already as revolutionary as the X-Files was at the time just when it came to how much we should distrust our government - something that prior to the end of the Cold War had been something we did almost without question - that might have been a bridge too far for 1990s viewer.
As to the larger question about Japan, I fear that much of the leftist ideology - argued about America' decision to drop the atom bomb was a sign of America's unjustified immorality - has done much to argue the narrative that whatever evils non-western powers do are either excused or considered lesser than the ones America and Europe have done.
https://davidbmorris.medium.com/how-truman-didnt-start-the-cold-war-interlude-d568d39b5b36
This article I wrote just a few weeks ago may be the clearest reason why so many historians choose to ignore the atrocities the Japanese did, particularly in place like Nanking. i'm going to begi following the author of this article because he has a similar sense of justice that we need to remember