I will however take this time to point out that the belief that the South was losing ground to the industrial North was contemporary to the period, not merely a modern construct - whether or not the belief was true has little bearing on the existence of the belief, nor whether it was part of the South's motivations. I wish that I still had a list of primary sources to direct you to, but it has been decades since I took the courses. There were people in the South who believed that they were losing freedoms (not merely in the ownership of slaves) as well as being targetted by the Northern states in an undeclared economic war.
Yes, 90% of the North was agrarian, though a good deal of its economic strength was central to the industrialized cities. As always there was a concentration of wealth - 90% of the populace does not equal 90% of the wealth. Much of the success of industrialization did indeed follow the war - new methods used to bore cannon barrels proved effective in the creation of high pressure cylinders for steam engines. However the railroads were already having an enormous impact on the United States, with the North considerably more heavily tied by rail. Factory work was often seasonal, moreso in the South than the North, textiles relied heavily upon the crops and were the first industries to make major inroads in the South. And even there the North had a large number of textile mills so that the South saw a steady stream of commerce leaving their states and heading north.
The rivallry between North and South can be traced to before the Revolution, to Adams, Jefferson, and Lee, each of whom hated the others cordially. In fact Adams last words were "Jefferson still lives." (False as it happens, they died within a week of each other, with Jefferson dying first.)
There were also voices in the South to abolish slavery, or at least loosen its chokehold on the economy. Oddly some of those voices belonged to slave owners... They could not compete if they released their own slaves and their neighbors did not, but if all the slaves were released then they could remain competitive. And as you say, a fair number were reluctant to break up the Union, not merely a political choice - there were still some fears of England taking advantage of the weakness a war would cause in the States. Many people remembered the War of 1812, if not the Revolution. I am not at alll convinced that those fears were groundless, though they were not in any way realized that I know of.
I honestly believe that the war would have happened regardless of freeing the slaves, but that by
not releasing the slaves the South chose to be the villains in the war. (Though some Southern states offered manumission to negroes who volunteered for military service.) And you are correct in that most Southern states had more volunteers in the Confederate Army than the Republic, the fact that there were any that differed shows that there was a lack of concensus.
The South did begin conscription first, but if I recall properly across the decades of my memory, it was not a unified decision - unlike the Union the draft was considered and ratified by the South on a state by state basis, less than half of the Confederate states had implimented it by the time the Union had unilaterally begun conscription. There were lynchings and riots in New York City, as some groups 'punished' the free blacks for causing the war. (People are idiots.) The Ku Klux Klan has its roots in the North as well as in the South, and sadly my home state was one of those places where it found fertile ground. (Again, people are idiots.) The south was a great deal less unified in its decision making than the North.
I think that the South was idiotic in opening fire on Fort Sumpter, and that by continuing the war for so long after their cause was lost they forfeited much of the sympathy that I, and many others, might feel for them.
For what it is worth I am a Northerner, have been all my life, and proud of it. At the time of the Civil War my ancestors were still in Ireland being persecuted by the English. My sympathies, for whatever they are worth at this far remove, lie neither with the North nor the South, but with the slaves.
The Auld Grump, fun argument.