This is the first paragraph of the Declaration of independence: When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation. By the principles upon which this nation was created, South Carolina had the right to leave.
I believe that rights come from our creator and not from a government. So, the people of South Carolina have the right to self determinisation. When government becomes so intrusive to the rights of the governed they can fight back. It seems to me that's our argument for the American revolution and our own fight for independce.