Slavery and the holocaust were both predicated on the simple idea that one kind of human was superior so I don't feel comfortable sitting around sipping tea and debating that.On the Holocaust I'd argue the opposite point -- it was the denial of Jews genetically having a higher IQ that helped lead to the Holocaust. Jews had a level of wealth and achievement disproportionate to their population. So if you don't believe they are smarter and don't believe they have earned it, then the explanation you are left with is that they are tricky and their gains were ill-begotten. And if you read Amy Chua's book World on Fire you'll see this pattern over and over again. A certain ethnic group (Jews, Chinese, etc) does better everywhere they go. But then get demonized by the local population for their overachievement, and pogroms result.
Slavery and genocide have been around forever, since we were chimpanzees really. The Romans were enslaving Greeks and everyone else (who they respected for their intelligence). Slavery was not invented because of belief in racial differences. Slavery was invented because people like taking the sh*t of other people.
The NY Times publishes hundreds of articles a year on racial disparities. If you're going to make it a big issue, then you need to fully explore the reasons for the disparities based on the facts. Otherwise you will get the wrong answers, and the wrong solutions.