You do realize that every state that seceded put secession to the people as referendum, and they OVERWHELMINGLY voted for it? Maybe you don't, you could be that ignorant.
South Carolina didn't. Their secession was decided by a convention. Kentucky didn't, they went the convention route, too. As did Mississippi. And Alabama. In fact only four states - Virginia, Texas, Tennessee, and North Carolina - submitted secession to a referendum. In North Carolina the referendum was defeated, but later the legislature took them into rebellion anyway. In Virginia the referendum actually was held a few weeks after the state was admitted to the Confederacy.
Maybe you don't, you could be that ignorant.
Or maybe just smarter than you.
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.