The Crimson Binome
Hero
I could swear that I've read at least one edition where absolute alignments were in effect for certain creatures. Demons and devils, in particular, are Always Evil because if they weren't Evil then they wouldn't be demons and devils.Sure - except that that's NOT what the rulebooks say. Nowhere in any edition of D&D will you find a statement to the effect that "If a creature is listed as having a particular alignment, every creature of that type that ever lived or will live has that alignment."
And just because orcs don't fall into that category in any given world, that doesn't mean it's true for every world. A setting where orcs are Always Evil is the sort of thing that a DM might want to implement, if they don't want the moral dilemma of killing orcs to come up ever.