I think both sides had valid points, but this is a very good example of the "Tyranny of the Majority."
The South thought the laws were unfair, but as the North benefited, and had the majority, they just didn't care what the South thought.
The tariff rate in 1860 was the lowest it had even been. The lowest. That is not what caused the war. When the Confederates congress enacted their own tariffs, they were basically at the same rate.
The South had been trying to secede since the 1820s, and their major complaint was always economic during that time period. I think the realization that Liberals had won control of the government to the extent that they did convinced them that more trouble was on the way, even if it was at the moment, temporarily lessened.
The “ South” was not at all a democracy. It was ruled entirely by the aristocratic elite in the Deep South. The fact that in the North, people who opposed slavery, even if they were in the minority, were able to exist, drove them nuts. The aristocrats did not tolerate disagreements. And like you, they believed their own BS about King Cotton. It’s a damn shame that 700,00 men from both sides had to die, but that is how history works. It can be very ugly.