Actually that is a moral question that is coming up in my PnP game. You see this priest, a very not evil priest, got a vision from his god, a good deity, that children born with a rune, either on the hand or on their face, will rise in power and destroy the city. The leader of these children will be is unborn child.
The PCs, not knowing the prophecy, have saved the lives of two children. Well, not exactly. They stopped one assassination and while the other became a very powerful undead but still has the mind of an innocent child which they rescued. Now if they learn of the prophecy I am wondering if they will side with the priest and kill these runebearers or stand against him knowing that they endanger the lives of thousands of people.