Something to think about.
Origins of Undeath
Numerous theories exist concerning the nature of undeath, and though some hypothesis compete with or contradict one another, others reinforce or overlap each other. While these conjectures may not agree on the origins of unlife, most of them at least assert that this condition is generally visited upon the bodies of recently deceased creatures. Below are some of the more widely accepted theories about the origins of this affliction
Atrocity Calls to Unlife: Evil acts can resonate in multiple dimensions, opening cracks in reality and letting the blight creep in. A sufficiently heinous act may attract the attention of malicious spirits, bodiless and seeking to house themselves in flesh, especially recently vacated vessels. Such spirits are often little more than nodes of unquenchable hunger, wishing only to feed. These comprise many of the mindless undead. Sometimes these evil influences also manage to reinvigorate the decaying memories of the body's former host. Thus, some semblance of the original personality and memories remain, though the newly awakened being is invariably twisted by the inhabiting spirit, resulting in an evil, twisted, and intelligent creature. However, this being is not truly inhabited by the spirit of the original creature, which has left to seek its ultimate destiny in the Outer Planes. This amalgamation is something entirely new.
Other times, atrocious deeds call dark, reanimating spirits into the fleshy form of the newly deceased, leaving the original spirit intact. This might happen if the person was already evil, or was tempted to evil in life. Alternatively, some good spirits might be unnaturally trapped within their bodies, slowly being perverted to evil as the dark spirits convert the body to undead status.
Negative Energy as a Supportive Force: While atrocity may serve as a trigger for unlife, it is nor enough to bring about a transformation of this magnitude on its own. It requires the very energy that drives dark spirits and their unquenchable thirst for life. That which is dead has no vitality, so where does the energy of animation come from? Negative energy - a force that is marshaled, stored, and utilized mostly by evil creatures, malign deities, and their servants - provides the power for this metamorphosis. Just as blood suffuses living creatures, negative energy suffuses undead, providing them all their abilities, from mobility to sentience, from flesh-eating to soul-devouring.
Negative Energy as a Draining Force: Some claim that undead exist concurrently on the Material Plane and the Negative Energy Plane. More precisely, they believe that undead on the Material Plane are linked to the Negative Energy Plane via a conduit, just as life itself somehow partakes of positive energy.
The Negative Energy Plane is the heart of darkness - the hunger that devours souls. It is a barren, empty place, a void without end, and a place of vacant, suffocating night. Worse, it is a needy, greedy plane, sucking the life out of anything vulnerable to its grasp. Heat, fire, and life itself are all drawn into the maw of this plane, which perpetually hungers for more.
The very existence of even the weakest undead produces a constant drain on the energies of the Material Plane, which accounts for sensations of cold often attributed to the unliving. As part of the enchantment of their creation, undead "siphon" a bit of the energy flowing from the Material Plane toward the Negative Energy Plane. This "stolen" energy serves to power their ongoing existence.
More powerful undead have a stronger connection to the Negative Energy Plane and are therefore able to siphon even more Material Plane energy for their own purposes before it is forever lost in the Final Void. This type of animation is known as necromancy, but it could also be called entropic animancy. Wizards speculate that magic might be able to link objects or corpses to the Positive Energy Plane, in this case reversing the flow of energy.
Undeath as Contagion: Many undead have methods of propagating their curse among their previously living victims. For instance, those infected by the diseased bite of a ghoul may contract ghoul fever. Those who perish from this rotting illness rise at the next midnight as ghouls themselves. In this way, some undead recruit the formerly living into their shuffling ranks.
Undead propagate in a sick parody of life's method of multiplying. Worse yet, undead proliferation is far quicker, easier, and doesn't require the consent of the creature to be made undead - only a victim's inability to drive off the grave-born attacker.
Purposeful Reanimation: Count on the knowledge-seekers to pursue too far the spark of life, and the dark fruits of death. Some seek death's secrets out of fear, thinking that by overcoming mortality, they will have no more to dread. Mages who tread this road to its conclusion sometimes embrace death completely, though they do not become immortal but simply enduring. Spellcasters who adopt this existence are commonly known as liches. To their sorrow, most find that forsaking all the pleasures of life while continuing to exist is a fate worse than the absolution of true death. Others probe the boundaries between one's last breath and the final silence solely for the sake of knowledge. Shorn of conscience or any passion other than the need to know the truth, these dabblers have been responsible for plagues of zombies, soul-snuffing winds, and other atrocities.
Sometimes these learned mages also experiment with animation of inert matter that shares many properties with the animation of undead, especially when the inert matter in question is composed of the cast-off body parts of once-living creatures. Such creations are commonly known as flesh golems. However, as similar as a flesh golem (or any other construct) may appear to a zombie, constructs and undead remain separate entities, for two main reasons. First, negative energy is not a requisite power for any common construct, including flesh golems. Negative energy does not energize constructs, nor does negative energy play a part in the methods whereby constructs can afflict foes. Second, constructs are not animated by evil spirits, but rather by elemental spirits. By some people's estimation, this similarity is too close for comfort, but most feel that the difference is great enough to warrant a clear separation of type.
Interesting Read if you really want to get in to undead
http://www.realmshelps.net/monsters/aboutundead.shtml
Regardless when you look at it Undead in Forgotten Realms are animated by Negative Force which is evil. No matter the intention of the person creating undead it is still an evil act.
(Edit) In regards to the Term necromancer it annoys me that people automaticly assume they are evil. The school itself does have a stigma to it but just because someone is focused on necromancy doesnt mean they go around animating the dead and such however it would be safe to assume they use spells that are powered by evil force.
(although if i remember correctly most healing spells were necromancy back in the older editions, later becoming conjuration)
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