Probably not. Not all Nazi party members were monsters or evil people either. But such is the ability of even decent people to do unspeakably evil things, especially when the culture is blind to it.
I wonder how many people today, who condemn slavery as evil, would have had slaves back then and not thought anything of it (and I believe it would equally apply if you reversed the colors). I also wonder what people in a future century will condemn us for doing right now...
I just don't think that you can compare slavery to what the Nazis did: the scientific, industrial disposal of people. Slavery had been going on for thousands of years.
You call slavery unspeakably evil, yet the Bible doesn't go that far. The Bible clearly condemns witchcraft and homosexuality, but then tells masters to be good to their slaves.
If it was so unspeakably evil, why didn't it make the Top Ten list?