Many northerners, even those who opposed slavery, saw white trash southerners as a dangerous breed. No less an antislavery symbol than Harriet Beecher Stowe agreed with the portrait penned by the Harvard-educated future Confederate Hundley. Though she became famous (and infamous) for her bestselling antislavery novel Uncle Tom’s Cabin (1852), Stowe’s second work told a different story. In Dred: A Tale of the Great Dismal Swamp (1856), she described poor whites as a degenerate class, prone to crime, immorality, and ignorance.
It's a fairly common viewpoint even today, what with To Kill a Mockingbird being a required reading classic (with its attendent portrayal of the Ewells as white trash) and memes of redneck guys marrying their sisters being fairly common.