Wait. I think I misunderstood you.
I realize now that you are criticizing the dishonorable wretches who were arguing on behalf of slavery.
Because, obviously, nobody would compare 19th century arguments against slavery with 20th century crimes against humanity.
Please no crap about "Humanity." I simply stated argumentum ad Baculum and its limits. I am indifferent to slavery and state without hesitation that no sane person today ever lost a meal or a nights sleep over the fact America had chattel slavery. I stated an historical fact not a moral judgement; ie. it was a northern commercial sentiment that attacked a agriculturally based near nobility that was a social factor in the causes of the American Civil war. The vast difference between Hamilton versus Jefferson and Madison illustrate my meaning
By the way is chattel slavery a "Crime against Humanity?'