Was South Carolina justified in seceding?

No, I don't believe so. They made a proclamation when they seceded, which is called the Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union, and stated that the main reason why they seceded was because they wanted to keep slavery, and were angry about their escaped slaves not returning to them.

However, if the question's about "are they allowed to secede?", the answer is yes, they are allowed to secede. If the question is about it being morally correct though, the answer is no.

Yes Carolina was Justified in seceding