I read with interest Ta-Nehisi Coates’ recent historical essay for The Atlantic, “What This Cruel War Was Over.” The article is worth reading. It consists mostly of quotations pulled from Southerner declarations, debates, and editorials from the Civil War and late antebellum eras, all on the theme of slavery and the desperate need to preserve it. One example Coates gives is the words spoken by James H. Hammond (then a South Carolina senator) on the senate floor in 1858:
The difference between us is, that our slaves are hired for life and well compensated; there is no starvation, no begging, no want of employment among our people, and not too much employment either. Yours are hired by the day, not care for, and scantily compensated, which may be proved in the most painful manner, at any hour in any street of your large towns. Why, you meet more beggars in one day, in any single street of the city of New York, than you would meet in a lifetime in the whole South. We do not think that whites should be slaves either by law or necessity. Our slaves are black, of another and inferior race. The status in which we have placed them is an elevation. They are elevated from the condition in which God first created them, by being made our slaves. None of that race on the whole face of the globe can be compared with the slaves of the South. They are happy, content, unaspiring, and utterly incapable, from intellectual weakness, ever to give us any trouble by their aspirations. 
What is most astonishing about this quotation (and the others like it that Coates cites) is how completely alien this kind of talk would have sounded to a Southerner living two or three generations before Hammond’s time.
One of the best books of American political or social history that I have yet read is William Freehling’s The Road to Disunion: Secessionists at Bay, 1776-1854. The book is a true pleasure to read. This cannot be said honestly about most historical tomes published over the last few decades, but it is true here. Freehling also manages to fill his book with insights about the nature of power and politics that are applicable to places and periods far removed from the antebellum South–long term readers might remember how I’ve used his observations to make sense of patterns in contemporary Salafist-jihadist terrorism. One of the major themes of Freehling’s work is the diversity of interests and opinions found in antebellum Dixie. The rough division between “north” and “south” we used today was much harder to draw in the American republic’s earliest days. As Freehling takes great pains to prove, there were many souths within the South, each with a different interest and attitude towards slavery. Slavery’s greatest defenders saw this with horror and dismay. They knew their peculiar institution would not be preserved into perpetuity until the many souths learned to act in concert as The South, united by a shared commitment to slavery. Creating this sense of unity and mission was a political project that took almost a century to complete. Surprisingly, their greatest challenge in radicalizing Southern society was the slave holding class itself. In the colonial and early antebellum eras the majority of southern aristocrats did not see slavery as something worth defending.
For example, here is what Thomas Jefferson had to say about slavery near the turn of the 19th century:
“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. Our children see this, and learn to imitate it… The parent storms, the child looks on, catches the lineaments of wrath, puts on the same airs in the circle of smaller slaves, gives a loose to his worst of passions, and thus nursed, educated, and daily exercised in tyranny, cannot but be stamped by it with odious peculiarities. The man must be a prodigy who can retain his manners and morals undepraved by such circumstances. And with what execration should the statesman be loaded, who permitting one half the citizens thus to trample on the rights of the other, transforms those into despots, and these into enemies, destroys the morals of the one part, and the amor patriae of the other…. And can the liberties of a nation be thought secure when we have removed their only firm basis, a conviction in the minds of the people that these liberties are of the gift of God? That they are not to be violated but with his wrath? Indeed I tremble for my country when I reflect that God is just: that his justice cannot sleep for ever: that considering numbers, nature and natural means only, a revolution of the wheel of fortune, an exchange of situation, is among possible events: that it may become probable by supernatural interference! The Almighty has no attribute which can take side with us in such a contest. — But it is impossible to be temperate and to pursue this subject through the various considerations of policy, of morals, of history natural and civil. We must be contented to hope they will force their way into every one’s mind. I think a change already perceptible, since the origin of the present revolution. The spirit of the master is abating, that of the slave rising from the dust, his condition mollifying, the way I hope preparing, under the auspices of heaven, for a total emancipation, and that this is disposed, in the order of events, to be with the consent of the masters, rather than by their extirpation.”  (emphasis added).
As in so much else, Jefferson’s words were those of a hypocrite. Jefferson’s life curse was to pen rhetoric that was powerful enough to inspire idealists across the ages while creating a standard he could never personally live up to. Not that this mattered much in the eyes of his contemporaries; a plantation master was never judged on what he physically accomplished. It was a man’s ideas and manners that mattered on the Tidewater, and Jefferson’s ideas were shared by many. Most intellectual southerners living at the turn of the century would willingly admit that chattel slavery was a wretched institution. They defended it on grounds of precedent and social stability: their society had not chosen slavery, the argument went, but inherited it from their British fore-bearers, and now that it was around it could not be done away with in a stroke without much suffering and misery. But there was a common expectation that slavery would end sooner than later, as economic and social forces slowly made the practice obsolete. This is exactly what happened in the state of New York. Southern gentry of Jefferson’s day expected that this would happen everywhere else–and that America would be better off for it.
Open celebrations of slavery like the sort Hammond offered would not become common until the 1840s. By the eve of the Civil War they were the only “politically correct” things a politician from the Deep South could say about slavery. I refer those interested in the story of how slavery’s most radical defenders were able to manipulate and mold southern society and culture until political elites across the region championed slavery as a positive good worth dying for to Freehling’s book. The point I would like to make here is a bit more basic. The American south of 1860 was more racist, more despotic, and less tolerant of traditional Americans liberties like freedom of speech than was the American south 1790. If you had pulled Jefferson’s grandchildren to the side in 1855 and asked them what the “right side” of history was, they would probably reply that it was the abolitionists, not the slavers, who were on the wrong side of it.
There is an obvious lesson here for all politicians and activists inclined to talk about “the right side of history” today. History has no direction discernible to mankind. Surveying current cultural trends is a foolish way to predict the future and the judgments of posterity are far too fickle to guide our actions in the present.
 James Henry Hammond, in Congressional Globe, 35th congress, 1st session, appendix, p. 71 (4 March 1858). Hammond’s speech is one of the more famous defenses of slavery as a positive good, but it is not the most sophisticated. For that see E.N. Elliot, ed., Cotton is King and Pro-Slavery Arguments, comprising the writings of Hammond, Harper, Christy, Stringfellow, Hodge, Bledsoe, and Cartwright on this important subject, (Augusta GA: Pritchard, Abbott and Loomis, 1860).
 Merrill D. Peterson, ed. Thomas Jefferson: Writings (New York: Library of America, 1984), pp. 288-291.
There was a lot of descent in the South about succession and going to war. If you consider that much of the Piedmont Region came down the wagon trail from Pennsylvania and went well down into Mississippi as small farmers, that isn't particularly surprising. The South's violent reaction to any counter argument within their own ranks I think further advances the case you make.