It's a truism because it's true: the Japanese couldn't fathom the idea of honorable surrender. When it came to their surrendering, they would only do it because their Emperor had ordered it, and even then a fair percentage chose suicide over surrender. When at the beginning of the war Americans, British, and Dutch chose surrender over annihilation, the Japanese considered it a demonstration of our lack of honor, and treated us accordingly.
Whether any Romans ever made it to Japan is highly speculative (Roman coins have been found in Japan, but anyone using the Silk Road could have brought them), but from the earliest times that Europeans arrived on Japan's shores in the mid-1500s, all Westerners have been nambam 南蛮, barbarians 蛮 from the south 南 (since they sailed up the Asian coast towards Japan). Incidentally, the "barbarian" character was originally 蠻, which is a snake on the bottom, out of the mouth of which comes words wrapped up in threads--very much like the Greek concept of barbarioi, or people who were too stupid to speak Greek and therefore sounded like "bar-bar-bar-bar" when they spoke. There was a Japanese nobleman during the war (I'd have to spend half a day digging through my books to find him) who said that he couldn't stand to hear Westerners speaking Japanese, something along the lines of how it sounded like a defilement of the language. Just as the Nazis treated non-Aryans as subhuman, the Japanese treated non-Japanese as subhuman, and Westerners as doubly so, simply because of how haughty we seemed to be towards them.
None of this should be construed as providing any justification for the horrendous treatment of POWs by the Japanese--they thought they were justified, and we had to place them in the position of annihilation or surrender to disabuse them of the notion.
Which leads to something I wanted to write yesterday and couldn't because of the Sunday schedule. James F. Byrnes should have been President at this time, since he was the one FDR wanted to replace Wallace on the 1944 ticket: he had been a Senator from SC, a Supreme Court Justice, and was instrumental in the FDR administration--FDR take Byrnes to Yalta. Truman became the Veep because the unions wanted him, and also because Byrnes had a racist streak a mile wide. Byrnes got his ideas about Japan from Grew, who wasn't blind to the atrocities the Japanese had committed but who probably, for want of a better way to put it, felt for the Japanese who had suffered in the atomic bombings. Byrnes already was beginning his falling out with Truman, and he was convinced that he was better at foreign policy than HST, though he was wrong about Japan, and later on he would be wrong about Iran, eventually leading to all the events in the last 70 years--the 1953 CIA coup because that was the only way to keep the Soviets out of Iran, which helped foment the 1979 revolution that we're still living with today, in part because of someone else who is convinced that he is smarter at foreign policy than the rest of us.
But that is for another time. The issue of whether Japan would have surrendered without the bomb is a fool's discussion. Of course Japan would have surrendered, but not on August 15, maybe on August 31 after the Soviets had taken over Hokkaido and all of Korea, killing 100,000 in the process, and then killing at least another half million during what would have been a 45-year occupation, just as in Eastern Europe--and that would have been better? Remember the Momotaro movie: as late as April 1945 the Japanese people were being prepared to invade the US, as silly as that would have been, so it took a REAL wake-up call to get the Japanese to surrender. My cynical side thinks that Byrnes just didn't like the idea of Truman being right.
If this was some kind of cultural trait, then why didn’t the Japanese mistreat the Russian POWs they seized at Port Arthur in 1904 or the Germans at Tsingtao in 1914? What little information I’ve seen about the 80,000 Russian POWs from 1904 is that they were held in camps in Japan, were adequately fed, clothed and housed, had access to reasonable medical care, corresponded with family, had religious services and recreation, and those that worked were paid for it. This was all before the Geneva Convention. After World War 2 Japan became a nation I would not suspect of mistreating POWs.
I still think there was something far more virulent and malignant at work in Japan during this generation.
The potential for such near-universal human behavior was created, of course, by God when in effect he forcibly separated men by confusing their languages (and creating the races) to disperse them post-Babel. Man's initial refusal to disperse had led to such constant horrific fratricide that the only solution was Noah's Flood. So, even though subsequently societies have so often been cruel to other societies, at least He has achieved His twin goals of first filling the planet and then secondly using that wide dispersal to enable the birth of the billions of humans He planned, so that many can enjoy Him forever.