The game doesn't portray brothers fighting brothers. It shows pieces on a map easing into firing range of one another with the objective of causing more casualties than they suffer.
It doesn’t matter if you play the light side or the dark side. People are still compelled to behave a certain way based on their circumstances, and individuality only really matters to the individual.
Nobody gets to be the hero, but everyone is important. Always Sometimes Monsters is personal, a bit meandering, crass, and occasionally more ham-fisted than it seems to realize.