He prominently supported the nullification movement led by John C. Calhoun, and argued in a series of court opinions that states in the Union were sovereign political entities, each possessing the right to reject federal laws it found unconstitutional.

The slaveholding South, he contended, had achieved a social balance that allowed for steady economic and technological progress, while avoiding the chaos of urban and industrial society.

Harper's assessment of other nations around the world confirmed this point of view: non-slaveholding civilizations in northern climates, such as Great Britain, were riven by inequality, political radicalism, and other dangers.

Harper's idea of slavery as a social good put him on par with Thomas Roderick Dew, James Henry Hammond, and other significant figures in the history of pro-slavery thought.

"[1] Chancellor William Harper quoted with enthusiasm from an article which said; "Slavery has done more to elevate a degraded race in the scale of humanity; to tame the savage; to civilize the barbarous; to soften the ferocious; to enlighten the ignorant, and to spread the blessings of Christianity among the heathen, than all the missionaries that philanthropy and religion have ever sent forth.