They show the intent of the parties to the constitution - the states. Nobody at the time claimed a state did not have a right of unilateral secession. The 9th and 10th amendments make it impossible to argue such a right would have had to be listed or that any powers not specifically listed belonged to the federal government rather than to the states.
The union is voluntary. States have the right to unilaterally secede. The federal govt will use force to prevent it but that is a position of “might makes right” - not one based on the original intent of the Founders.
Go on believing that fairytale if it makes you feel better. Just don’t act surprised when people look at you funny and say, “Say what?!”
James Madison did, among others.