The most memorable moment of “Nanking,” the new documentary by Bill Guttentag and Dan Sturman, comes in an interview with a very old man who, in 1937, was a young Japanese soldier — and a confessed rapist. Now he says he regrets his rapes, which were carried out at bayonet point on helpless Chinese girls. “It’s better when you’re both into it.”

I don’t know whether in Japanese his words have the translation’s wildly inappropriate echoes of today’s hook-up culture, but even if not, he is pretty clearly claiming some kind of retrospective self-justification from sexual freedoms that would have been scarcely imaginable at that place and time.

Such cold-blooded insouciance is a sort of latter-day equivalent of the plea of Marlowe’s “Jew of Malta” in mitigation of the charge of fornication: “But that was in another country, and besides, the wench is dead” — which, probably, the ex-soldier could also have said.

“Nanking” itself stands against such disingenuous efforts to minimize the significance of a horrible crime that is otherwise in danger of being forgotten as the last of both victims and perpetrators die off. Even the name of the city is retained from the 1930s instead of being updated to the more modern “Nanjing.” It helps to fix in our minds what happened there 70 years ago this week.

After the establishment of the Japanese puppet state of Manchukuo in Manchuria, in 1931, Japan had sought to further neutralize the power of the weak Chinese nationalist government, which was the only thing standing between Japan and complete dominance of China. Full-scale war finally broke out in July 1937, and by December, Japanese troops were at the gates of Nanking, then the Chinese capital. Fleeing Chinese soldiers threw down their weapons and tried to disguise themselves as civilians among the city’s ever-growing refugee population.

Under the pretext of seeking out the hidden enemy, Japanese soldiers burned and looted, murdered and raped their way through the capital for weeks. Estimates of the death toll range up to more than 300,000. The only slight check upon their murderous depredations was the presence of a number of foreign nationals belonging to then-neutral countries, whom the Japanese were mostly scrupulous about leaving unmolested. Many were American missionaries.

Messrs. Guttentag and Sturman have taken the letters and diaries of a dozen or so of these people, all of whom attempted, often successfully, to intervene and rescue individual Chinese, and hired Hollywood actors to speak their words to the camera, giving a first-hand account of the massacres.

Among the most impressive of these are Minnie Vautrin (voiced by Mariel Hemingway), the dean of a Christian girls’ school who faced down the Japanese and managed to keep her pupils out of the hands of the plunderers, and Dr. Bob Wilson (Woody Harrelson), a Harvard-trained physician who risked his life to give sanctuary to some of the fleeing Chinese soldiers in the American-run hospital.

Another is John Rabe (Jürgen Prochnow), a German businessman who saw his Nazi sympathies as being not only consistent with his humanitarian efforts, but useful to them by giving him leverage with the Japanese.

The stories of these Western observers are harrowing enough, but they are intercut with film footage smuggled out of Nanking by one of the missionaries, George Fitch (John Getz), as well as with interviews with survivors and a few of the perpetrators, such as the aforementioned rapist.

Not many who see this film will ever forget the emotion with which an old man describes how he was forced to watch as a Japanese soldier bayoneted his mother and his baby brother, still at the breast, when he was a small child. Yet on standing back a bit from it, you’ve got to ask yourself just what the filmmakers thought they were doing here by putting so much raw feeling on the screen. At the end, they say the film was made not out of hatred for the Japanese but as a reminder of “how horrible war is.” That seems to me a cop-out. It treats “war” as a force of nature and not as a product of human choices that can be both right and wrong.

Immediately after these words, a card informs us of Fitch’s pleas to America and other Western powers to do something to stop the Japanese atrocities. “But the world stood silent.” You can’t read that other than as a reproach, yet it is also an implicit demand that anti-Japanese forces should have gone to war, horrible or not. In other words, it’s not just “war” that is horrible, it’s the wickedness that war allows some warriors — but not others — to choose.

jbowman@nysun.com