Let's say you have two opposing factions, both having, more or less, extremely different views on a subject. For example: a society where people hate murder no matter if it's justified or not. They absolutely despise wars, and would rather be slaughtered than participate in one. Then you have a society that thrives on killing, where murdering is considered a sport, where if you want to be recognised as an adult you have to kill at least one person. Yeah, they don't make much sense, but I'm using those examples just to illustrate a point. How do you realistically portray both factions without appearing biased, without the reader going "Ah, so the author's a total hippie / psychopath bent on spilling blood?"