A game about combat needs a world full of things for the players to mow down but also not feel bad about killing, and sometimes you need a bunch of Violent Dungeon Fodder that can think and plan and make tactical decisions and potentially be negotiated with.

I’m a bit confused by this. Why not have them be any other species, or combination of them? If they’re capable of being negotiated with shouldn’t the players feel as bad about killing them as anyone else? I feel like “self-defense” can do a lot of heavy lifting in dungeon crawls, I’ve never really noticed my players feeling bad about killing bandit dwarves or whatnot.