My understanding is that necromancy does not necessarily mean reanimating the dead. One could study necromancy to combat those who use it for evil or if you use it to take life essence from your enemies to heal your allies, that seems in the same realm as siphoning and other such skills, just a different means of doing so. Or is reanimating always evil? Perhaps one could see it as full use of a creature, using its hide for clothes, meat for food and skeleton for service? With such a view it might seem wasteful or even unethical to not use the remains for some purpose.

Re-using the bodies of the dead is better than enslaving the living, isn't it?

To bring back their dead pet.

Necromancy itself isn't evil. You can practice and learn Necromancy without being evil. My Necromancer is actually not evil at all, despite being a Necromancer AND a vampire. The latter he became to have immortality while the former he uses to gain a deeper knowledge of souls, flesh, and soul gems which helps him in his efforts of being the best healer in Tamriel which can live on forever, always helping those who needs it from the shadows...

There is actually a NPC in ESO who practices Necromancy and is essentially a good lined character. Hell, when she uses Necromancy to summon a spirit, she doesn't lock the spirit and allow it to willingly communicate with her and you the player and allow it to leave at any time it wishes.