In the "The Mort You Know" category, I'd like to remind everyone of what necromancy really is.
In fantasy, it has been generally accepted that "mancy" means "magic" and "mancer" means "spellcaster". So, a necromancer is a death mage. But, in truth, this is not what mancy means. Mancy means divination. Go look at your friendly local new age hippy medium: oneiromancy (premonitory dreams), coscinomancy (reading in tea leaves), cheiromancy (palm reading), astromancy (a variant of astrology), crystallomancy, gastromancy or spheromancy (crystal ball gazing), hydromancy (with oracular lakes or fountains) and so on. The list is long.
So, why necromancy? Same thing as all others: it's predicting the future. And the necro bit comes from the tools you use to predict it, in that case, you predict the future by rolling or tossing bones, and by channeling the spirits of the departed to ask them questions.
Well, to be honest, if you're writing an epic fantasy story, it's not really spectacular enough. Let's change the definition. Instead of being a quack diviner, the necromancer will kill people with death magic! And animate the corpses as undead skeletons and zombies! And he'll turn himself into a spellcasting corpse to gain an eternal unlife! Now this makes for a cool villain.
And there you go. Necromancy is evil because it has been "retconned" by fantasy writers in order to be the evil villain's evil magic. You need to go no further.
Then you can deconstruct the trope to justify it. Somebody who wants to traffic with corpses and even become one himself can't be someone who's all right in the head. We've got, especially in the west, very strong taboos about playing with corpses. Did you know that for a very long time it was strictly forbidden to study human corpses? It could net you a trial for sorcery and then you'd end up hung. (No, not burned at the stake. Contrarily to common beliefs, the stake wasn't for witches but for heretics.) This explains why medical science in the Western world was really, really bad until some time after the Renaissance. Doctors had no knowledge of anatomy! Even today, a certain social stigma remains against undertakers and forensic doctors.
Agreed. However, The notion that 'Death magic' MUST be used for evil is challenged within the scope of the game world itself already. What I am surprised at, is why there is no vivomancy to go along with it. (reincarnation, flesh-mending, animation of inanimate objects, etc.)
The concept I picked up about magic in TES lore, is that magic in general is neither evil nor good. it is how it is employed that makes a particular spell evil or good.
Theoretically, A sadistic healer could kill somebody by healing them to death. (Imagine, magically induced cancerous tissue growth.) Does that make healing spells evil? Of course not.
Better is destruction-- A mage schooled in destruction could be employed to GREAT effect at a glassworks, for instance. The fire spells they wield allow for unnatural heat, without the need for mundane fuels, and could enable many spectacular crafts to be made (like ebony crafting, which requires magical heat.) Incidentally, the EXACT SAME MAGIC can reduce a person to smouldering ashes.
Just as destruction magick is neither evil nor good, Necromancy is intrinsically neither evil nor good.