To play devil’s advocate, I think understanding and being able to articulate why the ideas cited in this article are horrible (regarding slavery, suffrage etc.) is a worthwhile exercise. The response, particularly in an academic setting, to the question, “Why is slavery bad?” should not be “RACIST!” though that may be accurate. One should be able to make the argument, easy as it may be.
The moral and ethical case is clear and (nearly) universally accepted on slavery, but it was not 150 years ago, just as the case for women’s suffrage was not settled 100 years ago or for civil rights 50 years ago. We need to be able to make these arguments convincingly — maintaining consensus over the long run can sometimes be as challenging as building it in the first place.