Note that people who object to committing war crimes are not a kind of legalistic automata that require following the letter of the law no matter what. We do not always decide something is a crime because there's a law that says so. For example, the Holocaust would have been a crime even if the powers at the time had decided that it wasn't.

Complicated Chinese (and Japanese) laws about legal and familiar duty are really not the subject under discussion here, but a red herring. Murdering innocent people is an entirely different matter.

Finally, consider there are many people in this world who won't commit some crimes -- such as genocide -- even if there is no way out and refusing will cost them their own lives.