So I don't consider him to be much in the way of a constitutional scholar, and in any case, the right to independence is from a higher law than the US constitution which is mere man created law, and that only because the Declaration of Independence gave the newly independent nation the authority to create the constitution.
There is no natural right of independence! There is a natural right of revolution which is what the founding fathers appealed to in 1776. There is also a natural right of self-defense, so when a group of people invoke the natural right to revolution the people they are revolting from have a right to defend themselves to keep the country together. This is why the natural right of revolution is an appeal to force of arms or war. When you appeal to war you better have the power to make it stick.
Once you appeal to force of arms then your actions, in the western world at least, are evaluated under the concept of Just War. Let’s look at the southern rebels under the first criteria of Just War(which I received quite a bit of training on in the military), Jus Ad Bellum.
1)Proper authority and public declaration-were the southern rebels the proper authority and did they make public declarations. It could be argued they weren’t the proper authority, especially in states like Georgia and Tennessese where there was suppression of pro-union factions, but I’m going to give this one to the rebels. They did make public declarations. So point to the rebels.
2)Just cause / right intention- the southern rebels lost a free and fair election(even though republicans were kept off the ballot in the southern states) in a constitutional republic with a robust system of checks and balances. A party they believed would threaten their institution of chattel slavery won the presidency, though they still had enough representatives in congress to block most actions by this party, they decided to rebel. No way to sugar coat this, it is a horrible cause and horrible intention. Point to the United States.
3)Probability of success-or are the war aims achievable. Your not just wasting lives. The rebels chances of winning this war were slim to none. Point to the United States.
4)Proportionality-Did losing an election in a constitutional republic justify grabbing every governmental property in sight, actually imprisoning US soldiers and civilians, and firing on a US Fort. Answer is no. Point to the United States.
5)Last resort-was this the only means that the rebels had to protect their “peculiar institution”? No. They could have stayed in the United States and blocked most actions by the republicans. They could have worked through congress to pass legislation to allow states to secede or they could have seceded then appealed to the supreme court. They had many other options besides resorting to force. Point to the United States.
So under the Jus Ad Bellum theory of war its 4-1 in favor of the US. So the southern rebels fail under this test. Morally they were wrong to appeal to force of arms