To be clear, I can make a world where ogres are literally throws darts because it's a slow day at work dumb inbred mountain dwelling cannibals who terrorize entire nations and so on, and still not be saying slavery is a just action as a result of that low int. The very idea is abhorrent, and I'm not exactly sure why you think one would imply the other automatically. Are you implying that Ogres being dumb would be actual justification to enslave them?