I'm not thinking you are anything close to insensitive. I'm sure you, like I do, fully realize that just like all southerners don't have lazy grammar and diction, not all black slaves and freedmen spoke in pidgin English, though some at that time did. I imagine a percentage of white people without wealth allowing them access to or benefit of a good education probably did as well.
The book I'm currently reading is set in the early 1800s, with most of the characters being white settlers moving ever westward, written in the dialect of that time, much of which includes poor grammar as it seems the only form of education most of them have received was home schooling to a certain age and bible learning in their churches.
With regard to Sacred Hunger, I got the impression from that person's review that, being historical fiction, Frederick Douglass was included as a character with the author writing his dialect in pidgin English, as well. Since you've read it, I was just wanting to clarify if it was a just poorly written review, conveying a concept other than the reviewer intended.