Did you honestly think that, before the fel taint, the orcs somehow were such pacifists that they couldn't harm a fly? If that was the case, why would they even drink of the blood of Mannoroth to begin with? The blood wasn't to give them bloodlust, but to be controllable by the Burning Legion.
I mean, for crying out loud, look at some of the orc tribe names: Warsong; Laughing Skull; Shattered Hand; Bleeding Hollow; Bonechewer; Burning Blade... do those tribe names really sound like they belong to a pacifist race, and not a race where war and conquering was a big part of its culture?