In both volumes of that work, Freehling gives a great deal of attention to the narratives on both sides of the slavery debate and how they evolved over time. He identifies the Missouri crisis as an important moment in that evolution. The traditional justification of slavery in the US had been a paternalist one, that slavery was lifting backward African peoples up to the level of white, European civilization. This was a view reinforced by Enlightenment assumptions about the superiority of that civilization and of linear historical progress.
The cruelty of the institution and the barbarity of the international slave trade that supplied it were daily and hourly refutations of the notion that it was in any way notable, humane or generous. But that's not to say that some substantial number of whites didn't believe it.
At the time of the Missouri Compromise, Freehling explains that a different proslavery narrative was current, if somewhat geographically confined:
The ensuing southern public debate [of ], mirroring southern congressional speeches, demonstrated a section set against both permanent slavery and outside impositions to end temporary slavery. Only in South Carolina - so often, only in South Carolina - did a southern leader advocate perpetual slavery. United States Senator William Smith, anticipating later proslavery polemics, called slavery universal throughout history, sanctioned by the Bible, honored by the Greeks, needed by infantile blacks, and exalted by the South into a patriarchal relationship between master and slave. "No class of laboring people in any country upon the globe," soared Smith, "are better clothed, better fed, or more cheerful, or labor less" than our indulged serviles.After 1820, the "South Carolina" explanation became more common and then prominent, particularly in the Lower South states.
But in the Missouri controversy, Southerners faced a shift in the antislavery approach represented in New York Congressman James Tallmadge's proposals, which led them to embrace the "diffusion" argument previously used by opponents of slavery:
... the New Yorker's southern-style remedy [i.e., gradual emancipation] came accompanied with an anti-southern moral attack, an anti-southern bid for power, and the anti-southern idea that outsiders, not insiders, should decide slavery's fate. Tallmadge would furthermore abolish slavery not during the territorial phase of a region's development, as southern nonextensionists bad previously proposed, but during the statehood process. The shift in timing violated southern insistence that each state must decide for itself about slavery.But now they were ready to use it as a proslavery argument. One that became more cynical over time.
Southern attack on this Yankee poisoning of southern conceptions came accompanied with a crucial swerve in slaveholder thought. Speaker after southern speaker, in Congress and out, urged that spreading, not containing the institution would best create conditions for terminating bondage. This important so-called diffusion argument was not so much new as newly accepted. Land speculators, when seeking repeal of the Northwest Ordinance's ban on slavery extension, bad urged that diffusing blacks over midwestern areas would dilute southern racial anxieties and thus further racial reform. Most midwestern and southern proponents of the Northwest Ordinance had scoffed at this "liberalism."
Gradual emancipation, which Freehling also calls Conditional Termination, was intimately connected with the diffusion argument.
And he explains that it was very much connected with the association of slavery with the presence of blacks: "The Conditional Termination mentality was a vision of getting blacks safely out, of whitening a world, of removing the race to other plains."