Since you stubbornly refuse to understand what I mean by a "contingent decision" although I have explained it at least twice, let me try to get at it another way. Could (say) in 1861, a Southern jurist with a first-rate mind and thorough knowledge of the Constitution and Constitutional law have been able to anticipate the decision in Texas v. White, or rather that part pertaining to the legality of secession? Or was that decision dependent on particular views and beliefs of the justices who issued it and impossible to have been anticipated.
Since you stubbornly refuse to understand my position, although I’ve explained it several times, let me use your analogy. Do I think that the southern political leadership decided on their course of action knowing that it was illegal? No. But that does not change the fact that the Supreme Court later determined that they were wrong in their belief that unilateral secession was legal. It is not and it was not when the south took their action. The fact that the determination was made in 1869 means nothing because that is what happens in the appeals process. Scott v. Sandford, the famous Dred Scott decision, was heard by the Supreme Court 10 years after the facts of the case occurred. That doesn’t mean that Dred Scott entered into the process knowing he was in the wrong. But it does mean that in view of the court his actions were not legal. That doesn’t mean that the court is running wild creating ex post facto law, either. The court is not creating law, it is ruling on the validity of laws others have created.
I have no doubt that the southern leaders were convinced that they were in the right and unilateral secession was legal. It turns out that they were wrong. That doesn’t mean that they were committing some criminal conspiracy by their actions. It just means that they were wrong. Secession as practiced by Texas and the other southern states was not legal when they did it, it was not legal in 1869, and it is not legal now.