Time after time in the previous decades to 1860, Southern state represenatives, along with some of the Northern states made pleas in Congress to establish a more fair and equally just duty assessment - without any progress. So, there were from the second decade to the sixth of "cajoling, begging and pleading" with the government to equally tax. That's about the same time span of oppression from England the assembled colonies suffered. That's upon the same cause the American Patriots of the 18th century made their stand.
Tariffs were quite low from 1846. There was no need for Southerners to go "cajoling, begging and pleading" -- they largely wrote the tariffs themselves. Free elections -- and the Deep South Democrats' splitting their own party on the slavery issue -- brought the other side into office, and radical Southern Democrats didn't want to accept their defeat.
In 1860, those fire-eaters were already half-way out the door over slavery, and tariffs weren't a major concern for them. If tariffs had been their major interest, most likely a compromise would have been reached and there would have been no secession and no war.
It's not likely that a slavery-based Confederacy would have become an industrial superpower. Or that they would have become one any time soon, even if they gave up slavery. It's not what the secessionists wanted or intended either. Most of them were agrarians with an overconfidence about the power of cotton and the plantation economy. But would it have been a good thing if a slave-based economy had become an industrial superpower? Wouldn't that (quite unlikely) event have thrown the whole history of freedom off course and encouraged tyranny, slavery, and caste societies? Is it something we would applaud or encourage if it happened?
Did the North want to exploit the South for its own advantage? That may have been a result of the war, but I don't think it was any intention of Northerners. The idea was that higher tariffs would create an incentive to industrialize throughout the country. The intention wasn't to rob or beggar the South, but to shift the whole country, including the South to a sustainable path of industrial growth.
In this view, tariffs and the economic growth they encouraged would have helped to ween the South away from slavery. The idea was that protection would also have nurtured commercial classes that would bridge the gap between the rich and the poor, especially, though not exclusively in the South. There were some flaws in the protectionist approach, but was it so horrible an idea? If we oppose to slavery and applaud its demise, should we be so quick to condemn ideas that promised to lead the country up from slavery?
What we've seen in recent years is the growth of a confedero-libertarian view that doesn't always have much to do with the facts about mid-19th century America. Slaveholders benefited from a massive subsidy of uncompensated labor, a great violation of free market conditions, beside which tariffs pale in comparison.
The momentum for higher tariffs grew out of the Panic of 1857. It was felt that higher tariffs were needed to balance the budget and get the country out of the slump. This was probably bad economics, especially given what we know today. But it looks as though free traders allowed themselves to be divided over slavery and ceased to be as effective as they had been earlier.
There's a lesson in that for today's free marketeers: tie your cause too closely to things like secession and the Confederacy, overlook concerns with other forms of freedom and with the survival and continuity of free institutions, and you fatally weaken your cause. To count "free trade" or "state's rights" more than other, more basic freedoms and rights, is to make a mistake.