While I don't think Orcs are as a whole race, ''evil'', it seems when they're not kept in check, they always inevitably go nuts, or Sith Lord levels of bad, a more recent example being Garrosh, and all his mindless followers. Thrall is only level headed, because he was raised by humans, but not including him, most Orcs always go bad, or do mistakes that are often cleaned up by other races.
Discuss.