In this speech, Calhoun argues that slavery is a “positive good” for blacks. He makes this argument on a variety of bases.
First, Calhoun argues that blacks are better off in the United States as slaves than they ever were as free people in Africa. This is because, he says, of the innate inferiority of their race. They are so inferior that it is better for them to be cared for by whites in the US. As he says,
Never before has the black race of Central Africa, from the dawn of history to the present day, attained a condition so civilized and so improved, not only physically, but morally and intellectually. It came among us in a low, degraded, and savage condition, and in the course of a few generations it has grown up under the fostering care of our institutions ... to its present comparatively civilized condition.
Calhoun then says that the benefits of slavery are further proven by the fact that slave populations increase themselves naturally. These factors, he says, make it clear that slavery is good.
Later in the speech, Calhoun also argues that slaves are better off than free workers. This was a common argument in the South. It held that slaves were better off because they would be cared for by their masters and would be treated well since their masters wanted to protect their investments. This was in contrast to factory owners who did not care at all about their workers. As Calhoun says,
in few countries so much is left to the share of the laborer, and so little exacted from him; or where there is more kind attention paid to him in sickness or infirmities of age. Compare his condition with the tenants of the poor houses in the more civilized portions of Europe…
Thus, we can see that Calhoun feels that Africans are so inferior that slavery is better for them than freedom, particularly since they are much better cared-for than free laborers. For these reasons, he says that slavery is a positive good.