When you look at how American planters discussed slavery, over time, you find a marked shift. In the late 18th, early 19th century, slavery is is seen as an unfortunate inheritance, a problem of morality lacking a practical solution. Thomas Jefferson's articulation is probably the definitive in this school of thinking:
There must doubtless be an unhappy influence on the manners of our people produced by the existence of slavery among us. The whole commerce between master and slave is a perpetual exercise of the most boisterous passions, the most unremitting despotism on the one part, and degrading submissions on the other.
In Jefferson's day, talk of eventual abolition was not particularly rare in the South. Slave-owners spoke of colonization and some even emancipated their own slaves, The Quakers had a presence in the South and in the late 18th century banned slave-holding (If anyone has a precise date, I'll gladly insert.) Prominent slave-owning southerners like Henry Clay were in pursuit of some kind of compromise which would purge the country of its birth taint.
But by the 1830s, such thinking was out of vogue in the South. Men like Henry Clay's cousin Cassius Clay, once wrote:
Slavery is an evil to the slave, by depriving
nearly three millions of men of the best gift of
God to man -- liberty. I stop here -- this is enough
of itself to give us a full anticipation of the long
catalogue of human woe, and physical and intel-
lectual and moral abasement which follows in the
wake of Slavery.
Slavery is an evil to the master. It is utterly
subservient of the Christian religion. It violates
the great law upon which that religion is based,
and on account of which it vaunts its preemi-
In 1845 Clay was run out of Kentucky by a mob. By then the Calhoun school had taken root and Southerners had begun arguing that slavery was not immoral, but a positive good:
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.
In the meantime, the white or European race, has not degenerated. It has kept pace with its brethren in other sections of the Union where slavery does not exist. It is odious to make comparison; but I appeal to all sides whether the South is not equal in virtue, intelligence, patriotism, courage, disinterestedness, and all the high qualities which adorn our nature.
But I take higher ground. I hold that in the present state of civilization, where two races of different origin, and distinguished by color, and other physical differences, as well as intellectual, are brought together, the relation now existing in the slaveholding States between the two, is, instead of an evil, a good--a positive good.
This is not just a rebuke of abolitionist thinking, but a rebuke of Jeffersonian thinking. Fifteen years later, Alexander Stephens would call Jefferson out by name arguing that his presumption of equality among men was a grievous error.
Perhaps this is too crude an interpretation but the graph above, measuring the incredible rise in the wealth represented by the pilfering of black labor, tracks directly with the political debate. When slaves were worth only a cool $300 million, property in man was an "unhappy influence." When that number skyrocketed in excess of $3 billion, suddenly it was a "positive good." Perhaps this is to deterministic. I leave it to my fellow commenters to color in the portrait. At any rate the notion that such an interest--by far the greatest collective asset in the country at the time--could be merely incidental to the war is creationist quackery.
But on to the problem.