Right, this right here gets to the heart of my point.
Nekromanteía was not evil. Speaking to the Dead and recieving knowledge from them was not an evil act in the Greek understanding of what was going on. Dangerous? Sure. But so was walking outside the city limits or getting on a boat. We have records of the ancient greeks going to "necromancers" to call upon the spirits of the dead to ask for advice, or to find where they hid the family wealth. It was a common and accepted practice. As common as asking the gods for help.
But the biblical understanding was a little more complicated. The only dead worth talking to were in Heaven, and that was God's domain, and you didn't summon them, God sent them. So the idea of using this magic BECAME dangerous and forbidden and evil. But the root of that was black magic, the magic of doing harm with evil spirits. Which is VASTLY different than summoning a wise spirit to ask them for advice on how to survive a catastrophe.
There seems to be two unrelated points.
The meaning of "necromancy" has little to do with healing. I prefer Heal and Resurrection as part of Abjuration.
On the other hand, I agree, necromancy can be ethical, at least situationally.
The biblical prohibitions can relate to certain ethical problems, but can also relate to ethically neutral ceremonial taboos. Anthropologists demonstrate that every biblical taboo relates to mixing a symbol of life with a symbol of death. Famously, the prohibition against mixing milk and meat is mainly nonbiblical but coheres with the cultural biblical pattern, where the milk corresponds to nourishment and life and the meat corresponds to killing and death, whence the symbolic taboo against mixing them together.
In the case of the undead, the ghost itself is a symbol of death while speaking with it is a symbol of life. Thus there is cultural taboo against mixing two. The prohibition appears in a context of concerns about invoking powers other than the Divine, but mainly this prohibition is symbolic. Biblical contexts include ancestor veneration, especially of Avraham, Yitskhak, and Yaakov, but these are "kosher" when in the context of invoking the Divine and the sense they are genuinely alive with the Divine. Thus there is no "death" mixing with life.
But these finer distinctions were often lost in medieval contexts, where anything prohibitive was viewed as if "evil". Thus they conflated the ethically neutral
necromantia with evil spirits of
nigromantia.
In the context of D&D, the dark side of Necromancy including its spooky undead and full-on evil fiends and modern cosmic horror of aberrations is part of what makes it fun for a fantasy game. One can look at the Warlock class to see the appeal.
It is possible to wield Evil powers for the sake of a Good purpose. Plenty reallife folklore from various cultures makes this point.