The Tavern

If regeneration is evil necromancy, healing potions should also be evil necromancy. It's a bizarre inconsistency. TSO characters can take the hit.

If all healing is necromancy, then TSO's heal on kills is necromancy, and therefore TSO is a fallen god, and all is death and lies.

Necromancy is obviously god power stolen from the good gods by Kiku and bestowed upon mortals in spell form, that's why it's "Evil" (Where the crawl definition of "Evil" is "Something that TSO doesn't like")

Yeah - the issue isn't healing, it's that you're messing with the natural order of things. Healing is the domain of the gods.

And also potions. And Deep Dwarves. And the 5 key.

...and a random unexpected Mutation (just to throw in the evolutionary perspective)

Heal wounds potions being evil makes sense because of already listed reasons. But Curing potions primarily exist to cure poison and toxic, the healing is mostly there to undo the recent poison damage and I would be fine with it not healing at all if you haven't taken poison damage recently (from a flavor perspective). Balance-wise, early game poison and toxic kind've suck and are irritating to deal with (namely bees) without access to Curing and this could force good aligned players to learn cure poison (or break conduct) if Cure potions were evil. Thus if Cure potions being evil is your proposal, all good aligned gods need to provide curing to compensate.

I have never understood why Regeneration is Necromancy.

^Necromancy!

The Shining Eye gazes at you.
You feel jittery.
You feel robust!
You feel guilty for feeling robust.