What did John C. Calhoun mean when he said slavery was a "positive good"?

Calhoun literally meant that slavery was a "good" rather than an evil. A senator and leading defender of slavery, he described the institution of slavery in this way many times, growing more and more strident in its defense as the abolitionist critique in the North gained popularity. Calhoun said that "never before has the black race of Central Africa. . . attained a condition so civilized and so improved, not only physically, but morally and intellectually" as it had under slavery. He argued slavery was not a "necessary evil" that would one day be eradicated, as some previous generations of slaveholders argued. He said slavery was the best labor system and the best way to structure society. In a common trope among slavery's supporters, he compared slavery favorably to the conditions faced by factory workers in the North, which he said created a dangerous working class which led to "disorders and dangers" in any industrialized society. Calhoun went on to argue that if the institution of slavery was threatened, the people of the South would defend it by leaving the Union, a right they were increasingly beginning to claim for themselves. Slavery and abolitionism, Calhoun asserted, could not coexist. Calhoun's views increasingly became dogma among the planter class in the South as midcentury approached, a development that contributed to secession and civil war.