I guess the best way to test that claim is to begin at the beginning.
On December 20, 1860, a "convention" of South Carolina bigshot "delegates" approved a secession declaration. When did South Carolina hold this "referendum" that you describe?
There are 12 homes and about 19 adults living on my cul-de-sac. If 15 of us want our cul-de-sac to secede from the United States so we won't have to pay U.S. taxes anymore, we can vote to create our own nation, I guess? And, the 4 who vote no are just going to have to accept our decision as binding on them? What shall we tell the mailman?
As you will learn if you try it, no cul-de-sac, no homeowners' association, no town, no city, no county, no state can declare a "secession" and thereby deprive any other American citizen of his/her citizenship or his/her rights under the U.S. Constitution. The Constitution creates political bonds between "we, the people of the United States" and we, the people of the United States, are committed to protecting one another's rights as American citizens.
No, there is no such thing as a legal "secession" even if it's to protect something as important as the institution of slavery. "Secession" is just a parlor word for revolution.
A childish argument to say the least. States are defined in the USC. Entire states can move to secede. This infantile argument that you espouse shows how little you really understand of US history . It also show contempt for the lives lost in a serious struggle and the honor and integrity of Southerners everywhere.
You are neophyte compared to other Lincoln apologists. You should keep quiet and read these posts and try to learn something, you're not ready for prime time. Please stop; this is embarrassing - to you. You are unworthy of my time.