Bu Lai En: it's true that those codes are often ignored, but the fact that they exist at all acts as a brake on the worst excesses. When breaches do occur, the do at least register
as breaches and cause shame to those involved. And I wasn't thinking of "chivalry", either in the west or in pre-war Japan, which was indeed just a ritualisation of violence. I was referring to the basic understanding that war is "politics by other means", and is fought between armies, not between peoples. And obviously those codes don't make war any less disgusting, or less likely to happen - I never said that. What they do is ensure the genetic survival of the societies involved, and they minimize (NOT eliminate!) the depth of psychological trauma involved. That's about the best that can be expected.
An interesting example was the behaviour of Russian soldiers during WW2, who were famous for their shocking behaviour (in some instances as bad or worse than the Japanese). The Russians, at that point in history, were a traumatized people. Many of the traditional social restraints on (for example) murder and torture had been removed by the Revolution and its aftermath. A counterpoint might be the behaviour of the British in colonial India, who were racist and treated the Indians as inferiors and slaves, but outright cruelty and abuse was (relatively) rare, despite the fact that they could (in theory) do what the hell they wanted with impunity. The only restraint was the British social code that said certain things are simply "not done".
It's also important to stress that the Seediq were most emphatically NOT "fighting for survival". They were kicking back against the petty - and relatively minor - cruelties of occupation and exploitation. They sat around moaning about how they were "losing their culture" but I couldn't figure out what aspect, precisely, they were most bothered about; they didn't seem to have
a culture to lose. They didn't seem too worried, for example, about the Japanese trashing their environment and carting off all the trees (although I guess they didn't comprehend the scale of it). Ultimately, they could have survived with culture and gene pool more-or-less intact by simply disengaging from the Japanese (as far as possible) and keeping a low profile - which is exactly what Mauna tried to convince everyone to do. The Japanese were using them as unpaid labour and no doubt meting out arbitrary "justice" (I was surprised how little of that was depicted in the movie), but generally speaking, the Japanese occupiers just wanted a quiet life.
It makes pefect sense that if you're fighting for survival you send in every man, woman and child you have to kill every man, woman and child you can of the enemy, by any means at your disposal. It may seem barbaric to us, but it makes perfect sense in an historical context, and in the long run, is far less barbaric than the 'civilized' killing carried out by the so-called 'honourable' socities.
I understand your point, and yes, in extremis, you're right. But that wasn't the situation here; more importantly, it could not have worked
. The outcome (genocide) was completely predictable. And examine your reasoning from the Japanese point of view: although they were the invading group, the massacre confirmed their view that the Seediq were barbarians, and therefore the only logical response was a barbaric one.