If you read the causes that South Carolina used to justify their secession, and still think that slavery was not [THE] main reason they wanted to become a separate nation, then I don't think anything would change your mind, slavery is becoming an issue that people from all the states could not ignore and South Carolina's economy, and the wealth of those holding the offices of the state, depended upon slave labor, they did not want to see their wealth taken away as it surely would have been when the institution of slavery was destroyed. If it was not the main cause, why is it mentioned throughout. They wanted to become a separate nation just to keep slavery in place.
From South Carolina Declaration of Secession:
A geographical line has been drawn across the Union, and all the States north of that line have united in the election of a man to the high office of President of the United States, whose opinions and purposes are hostile to slavery. He is to be entrusted with the administration of the common Government, because he has declared that that "Government cannot endure permanently half slave, half free," and that the public mind must rest in the belief that slavery is in the course of ultimate extinction.