I think it's also somewhat useful to think about "the other side" when holding a certain position. Of course, it may not be based in reality, or be factually incorrect as to why someone else holds a different viewpoint. I believe it's still worthwhile as a thought experiment to try and understand an opposing point of view, even if you'll never agree with it. There can still be some compassion or common ground, especially when it comes to something so life-affecting as war.
I do agree that authors can only write things they themselves believe, or at least are marked with their own way of thinking, even when trying to guess or infer the reasoning behind someone else's differing belief or opinion. When I get in a heated discussion online, and I can tell that someone is angered just from me stating my opinion, I've often tried this thought experiment to at least not take things personally if someone comes after me with violent or explosive language. I'm sure you've probably experienced it yourself, but some people online seem to hold their own beliefs as law, and will act out when challenged (even when your intention wasn't to challenge, but just to state your own opinion).