The horde and alliance factions are "racist." Why can't a human decide he wants to be with the horde? Why can't an orc decide he would rather fight for the alliance? The only orcs that need to redeem themselves are the ones that did the bad actions the rest of the orcs should not be "tainted" because of what other orcs have done. Even then, everyone else needs to forgive anyone, orcs included, to properly move forward anyway.