What is the fundamental argument that Calhoun is making in "Slavery: A Positive Good"? What evidence does he use to support his points? How do documents such as these help us undertand American society in the 1830s?

Calhoun's fundamental argument in "Slavery: A Positive Good: is that the south must not make any concessions to the abolitionist north to defend the institution of slavery, which is, he writes, "a positive good." Calhoun predicts (accurately, as it turned out) that the abolitionist sentiment in the north, if left unchecked, would lead to conflict with the south. He writes, "the conflicting elements would burst the Union asunder, powerful as are the links which hold it together." In other words, abolitionism would go on to cause a rift between the north and the south.
Calhoun defends slavery with different points of evidence. He writes that slavery is a condition that has existed throughout history. In his words, "I hold then, that there never has yet existed a wealthy and civilized society in which one portion of the community did not, in point of fact, live on the labor of the other." He thinks that southern slaves are treated better than the laboring classes in other nations and that less is expected of them. He also contends that slaves are treated more kindly if they are sick or old than are the laboring classes of other countries. He also believes that the relationship in the south between the slave and master provides for a freer state than the conflict between labor and capital in the north. 
Documents such as this one help us understand the conflict between the north and south and the deep-rooted nature of their tensions. How do you think this document shows the economic, philosophical, and sociological differences between the north and south in the 1830s?