"There is evidence that suggests slavery was beginning to die out on its own. For example, the percentage of Southern whites who belonged to slaveholding families dropped by 5 percent from 1850-1860" (Robert Divine, T. H. Bren, George Fredrickson, and R. Hal Williams, America Past and Present, Fifth Edition, New York: Longman, 1999, p. 389). Nevins noted that "slavery was dying all around the edges of its domain" (The Emergence of Lincoln, Volume 2, p. 469).
Slavery was dying around the edges. But not in the 15 States were slavery was legal. The 1850 census records 3.2 million slaves in 15 out of 31 state. The 1860 census records 3.9 million slaves in 15 out of 34 states. The slave population was growing, not dwindling in the states were slavery was legal.
"Our position is thoroughly identified with the institution of slavery-- the greatest material interest of the world. Its labor supplies the product which constitutes by far the largest and most important portions of commerce of the earth. These products are peculiar to the climate verging on the tropical regions, and by an imperious law of nature, none but the black race can bear exposure to the tropical sun. These products have become necessities of the world, and a blow at slavery is a blow at commerce and civilization."Hardly the statement of people who think the institution is fading. More like a statement of an inability to even imagine a world without slavery.