South Carolina was the very first. States like Virginia were objecting more in principle to the idea that South Carolina couldn’t leave if it wanted to. So, the determining factor remains slavery. No dispute over slavery, fugitive slaves, etc. no secession.
It is good of you to acknowledge that Virginia was clearly guided by the principle that states had a right to independence. It's a shame that the rest of them did not recognize this right.
So, the determining factor remains slavery. No dispute over slavery, fugitive slaves, etc. no secession.
You are begging the question here.