ToME: the Tales of Maj'Eyal

The status quo on this is astoundingly frustrating. I'm doing the final fight right now and Aeryn attacked me with an AOE spell. She had Empathic Hex on her, which made me do a fraction of her damage back to her - and this was enough to set her hostile.

This isn't an isolated case, either, as knockbacks are similar. It's particularly bad when using Unseen Force because the knockbacks hit a random enemy in a random direction.

Well it really depends on which NPC.
In aeryn case I agree yes

I don't think any quest-related NPC should go hostile if you hit them while fighting something else on screen.

Or if the fools wander into your AoE DoT attacks of their own dumb accord...

I don't know, I might be pissed if you hit me even if it were my fault. Perhaps some NPCs could be more pissy than others? That would be funny.

you could use already implemented system of factions like each 5% of hp damage dealt gives -15 to personal relation