I agree with Norman Ravitch, and for a reason that may shock many of you. He draws attention to the Holocaust, whose victims were not desired as workers, but as corpses. I say look away from antebellum history and mid-20th-century history to the corpses we are making in our very own oppression of the innocent. Nobody has any right to condemn slavery unless they condemn abortion.
As World War II was drawing to a close, Pope Pius XII, quoting St. Augustine, said: "Change the heart and the [work] will be changed. Eradicate [greed] and plant charity. Do you want peace? Do justice, and you will have peace. If therefore you desire to come to peace, do justice; avoid evil and do good. This is to love justice; and when you have already avoided evil and done good, seek peace and follow it." (Communium Interpretes Dolorum)
In other words, get the beam out of our own eye before condemning the mote in our dead ancestor's eye. Otherwise we are just moralizing poseurs.