Lets get one thing straight. Slavery is abhorrent. Indeed I believe there's a good legal argument that Amendment V to the Constitution prohibits it.viz " ..nor shall any person be ....deprived of life, liberty or property without due process of law..." Were slaves deprived of their liberty? Yes. Was it done by due process of law? No. The fundamental question was can a person be considered property and my answer is no because, if one can, anyone can. While I believe the Southern States were legally correct, morally they were wrong.
What I'm anxious to establish is the right to seccede because a Federal government which requires you to buy health insurance is most certainly acting "Ultra Vires" the powers granted to it by the states under the Constitution.