Then surely you can present a couple of quotes from southerners saying that that's why they're seceding. Maybe you could look in the declarations of causes that four of the states issued. Oops, they pretty much only talk about protecting slavery.
From what? The Constitution? No, the Constitution guaranteed slavery. Lincoln? No, he would continue slavery in order to preserve the union. From Northern abolitionists? No, there were just a handful and mostly in New England. From an army fighting to end slavery? No, the army was fighting to preserve the union. So why would an entire region secede because of slavery if what they were seceding from would not have prevented slavery?
Per chance you have never read the speeches given on the floor of the US Senate and the House before secession began. I suggest you do that and pay particular attention to the speeches given by the Southern Senators re: shipping of cotton, tobacco, rice, sugar cane, etc. When you figure the freight rates utilized at that time, you will see the disparity involved, done solely to protect the Northern farmers and factories. Each of the Southern states had reasons for seperation,(none good though)and the rhetoric at that time was slavery and ownership of same. My great Grandfather wrote in the family bible his reasons for fighting for the South, and nowhere is slavery mentioned other than for his being against "any man owning the body of any other." Gee, sounds like a real slave owner to me, what do you think?