Walt, I don't disagree. But after all your time on the sort of threads are you saying you have never encountered someone who does not accept this premise?
My point is that arguments based on your premise above, or the opposite one in the original article, are not going to sway the other side. The premise itself must be commonly accepted first.
Those who ignore this, and try to build further persuasive arguments without addressing the premise itself, are guilty of the logical fallacy "begging the question."
Most of the CSA apologists use natural law arguments and sources to counter U.S. law and the words of the founders professing the permanance of the Union.
I doubt they really believe that secession was legal under U.S. law.
Walt