In my case, the question is due to a group of undead that want to re-build their long-destroyed city, for which they will need living population. The undead aura is quite a problem in that regard, so they have tasked one of theirs (a former healer) to solve the problem with magical research.
In my game world, "evil" is not a state of mind but just a label to denote certain spell lists that come from a specific source, so an undead necromancer is by no means an evil being, just someone who used a certain type of magic. The rumors on the game world are that this kind of magic makes you mad, but it's just superstition.