My Pathfinder group and I came upon an interesting quandary the other night after our party had sacked the evil temple of the frog god near Rappan Athuk.
The priests there were in the practice of kidnapping a few local peasants semi regularly for sacrifice. Our party, of course, assaulted the temple, killed all the priests we could find, desecrated the altars and idols, etc., and freed a handful if prisoners.
The quandary was this: in a fantasy world, where magic exists that can heal wounds and cure diseases, were these priests sacrificing peasants a necessary part of the circle of life, and hence killing them an evil act?
One position was that they were serving the role of predators, limiting the growth of the local population. Without that predation, the population of the area would grow exponentially, and quickly deplete the area’s resources in only a few generations.
The counter position was that natural selection in a fantasy setting is replaced with supernatural selection. There are all forms of humanoids, monsters, and extra planar beings, on addition to bandits, marauders, mercenaries, and other warring factions to consume any surplus population.
Both of these positions have merit.