This has become dogma throughout Academia ever since the 60s leftists engaging in their long march through the institutions became dominant around the late 80s/early 90s. I was educated in private high schools, got my undergrad degree at the University of Florida, my law degree at California Western and my MBA at Thunderbird. Of those only UF is public, but the point still stands.
In college and after, I read not only contemporary accounts of the Civil War and Southern history, but also older ones that have been forgotten or fallen into disfavor.