Slavery for blacks, the south declared, was the surest guarantee of "perfect equality" among whites, as they liberated them from the "low, menial" jobs like factory labor and domestic service performed by wage laborers in the north.

This statement is true as in the old times, the North ans South were proslavery because they feel that they will be liberated from the "low, menial" jobs like factory labor and domestic service performed by wage laborers in the north. It was the only plausible explanation for the North by guaranteeing equality for whites. Also, they believed that without slavery, the whites would never achieve their civilized pursuit due to these menial jobs.