I bring up the Holocaust merely to illustrate points, not about what the Nazis did, but to reveal the process by which they did it. Nazis believed that the law was what they said it was. And that is why they were hung, and rightly so. There are some things that are wrong no matter what the law may say. But you devote a great deal of your book to covering the issues surrounding slavery.
Slavery is different.
It can be fruitfully discussed. Slavery creates a relationship in which one party abuses its power. In nineteenth century America, it was whites over African-Americans, but there have been many kinds of slaves between Pharaoh and Jefferson Davis. Society now agrees that a person of color has as much right to liberty as a white person. It was wrong to enslave humans 300 years ago or 3000 years ago.