@ElizaBennett - I agree with you, it's hard to believe, but absolutely real. Teaching middle school in the Deep South, I encountered students who were confused by a play we were reading about Harriet Tubman - because they thought that really most slaves were pretty happy. So why would they want to run away?
I remember looking to the song issue when it was news. Apparently, it was written by an educated African American man who had been born free, and some people think it's not meant to be taken literally. It could be satire on the difficult conditions facing newly freed slaves, who had so much trouble finding work that slavery could almost be appealing in contrast, or it could be ironically expressing the feelings that some whites *wanted* freed slaves to have.
Not that that's why some people defended it. I think it's just hard for people to look horrible things in the eye, and so some Southerners still want to romanticize the days of hoop skirts and cotton plantations and think that everyone was happy.