Which is why the premise for the piece being analyzed here is bogus. If secession was for the purpose of keeping southern slaves in bondage then perhaps there is a slim rationale for the argument. Otherwise it's simply historical revisionism with a new twist. It's meant to justify actions which were not otherwise justifiable.
LOL. States' rights is just what you describe, as anyone with even a rudimentary understanding of history knows. The South seceded because their leaders wanted out. They had wanted out for a long time. Some of them never really wanted in. They never liked the Constitution. Patrick Henry was a typical slaver. He acknowledged early on that the Constituion spelled doom for slavery. He professed to hate slavery, but he practiced it, and thought it "imprudent" that it ever--ever--be abolished. It was men like him who seized whatever excuse was handy to try and destroy our government.