Slavery wasn't the big concern. The Morrill Tariff was. It was going to pass the Senate. It had already passed the House. Lincoln was a huge proponent of it. Southerners had already seen how damaging the Tariff of Abominations was to their economy a generation earlier. Now those tariff rates were going to go right back to ruinous levels. They had had enough. Though it isn't the moral feel-good cause its portrayed as now, slavery was just the excuse for the Southern states to leave and it was the very first bargaining chip the Northern states offered to sacrifice. It was money both sides were actually interested in.
I see somebody has fallen off the wagon again.