I'll give a small bit of background on slavery during these two time periods first.

Slavery was sort of the norm back in the 1700s. Congress in 1807 decided to outlaw the Atlantic slave trade starting in 1808, but there were already so many slaves in America by then that the slave population could sustain itself. In fact, free and enslaved blacks outnumbered whites in Charleston, North Carolina. Slaves were essential to the cotton industry, which was the centerpiece of the Southern economy. Although most Southern farmers by 1860 were yeoman farmers (they owned a small plot of land, compared to huge plantations like in Gone With the Wind), slaves were the thing to have. Yeoman farmers set aside money just so they could save up to buy a slave, because the idea was that if you couldn't afford a slave, you were basically worthless. When the nation was founded, Southerners thought slaves to be essential to their freedom. They showed this by demanding slaves (who were property) to be given representation (something property can't have; it's quite the hypocrisy) in Congress. The Three-Fifths Compromise counted one slave as 3/5 of a human. With sufficient representation in the South now guaranteed, Southern slaveholders could go about their business. It wasn't until the nation began to expand beyond the Appalachian Mountains that slavery became a real issue.

By 1860, the issue of slavery was heating up, but not in the sense of emancipation. The Civil War did not start out as a war to end slavery. Instead, the concern was the institution's expansion into the American West. From the beginning of new states entering the Union, a concern was always if it would be a free state or a slave state. The reason for this was one faction would have more representation over the other in Congress and legislation would then pass in favor of whoever had the advantage in numbers. That's why you see things like the Mason-Dixon Line, the Compromise of 1820, and the Wilmot Proviso as ways to keep that balance of free vs. slave.

So where does that leave us with your question? Well, by the time 1860 rolled around, the issue of slavery was being forced into politics. Should slaves be allowed in the territories? Should the territories themselves decide? (see Bleeding Kansas for your answer) If anything, a time-traveling slaveholder coming from 1789 might be amazed at how much opposition there would be to slavery. Perhaps you would be surprised by the clear distinction of free North and slave South. I'm sure you both would agree that it was your right as a voting, land-owning, law-abiding, God-loving, American citizen to own slaves and do with them as you please, even if that means settling in the West. If there was any disagreement between 1789 dasunt and 1860 dasunt, the differences wouldn't be overly large and could be attributed to the seven decades in between.

The main difference is a transition from the "necessary evil" rationale of the American War of Independence and the "positive good" argument in vogue by the time of the Civil War. The philosophical consensus of slaveholders in the American South (at least the vocal ones) was that slaveholding was undoubtable evil. Washington, Madison, and Jefferson all denounced the evils of slavery while simultaneously holding slaves. They detested the institution for two primary reasons: intellectual distaste and resentment. They saw slavery as outdated and that a reliance on slavery could damage the moral integrity of the white men who owned slaves. But they also resented that they put all their eggs in one basket by living in a system entirely dependent upon slavery. Jefferson famously referred to the South's addiction to slavery as "having a wolf by the ears" in that they could neither safely hold on or safely let it go. Having said this, They also believed that slavery were simply evaporate with time, like all outdated systems. They did not foresee that slavery would only strengthen its grip on the South as time went by.

As the years went on, the Northern arguments against slavery became more moral and ethical than intellectual and economic (though those arguments hardly disappeared). The Southern argument changed with it and from this change came the idea that slavery was a "positive good" rather than a necessary evil. They increasingly endorsed the idea that the slaves were improved by their bondage as it had removed them from the barbarity of Africa and placed them in the "civilized" American South. They also believed that, as an inferior race, slaves were not fit for freedom and needed the moral guidance of the benevolent slaveholders or else fall into depravity and moral and economic decay.

By the time of the Civil War, the Southern consensus had entirely rejected Jefferson's concept of slavery as a necessary evil. Confederate Vice President Alexander Stephens famously outlined this concept in his "Cornerstone Speech" delivered on March 21, 1861:

Jefferson in his forecast, had anticipated this, as the "rock upon which the old Union would split." ... The prevailing ideas entertained by him and most of the leading statesmen at the time of the formation of the old constitution, were that the enslavement of the African was in violation of the laws of nature; that it was wrong in principle, socially, morally, and politically. It was an evil they knew not well how to deal with, but the general opinion of the men of that day was that, somehow or other in the order of Providence, the institution would be evanescent and pass away.

He went on to say:

Our new government is founded upon exactly the opposite idea; its foundations are laid, its corner- stone rests upon the great truth, that the negro is not equal to the white man; that slavery -- subordination to the superior race -- is his natural and normal condition. This, our new government, is the first, in the history of the world, based upon this great physical, philosophical, and moral truth.