Not so. Remember this?
[Amendment X]
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Nowhere is the power to approve/prohibit a State (or even SEVERAL States) from leaving delegated to the United States or prohibited to the States. Since the Federal Government was a CREATION OF THE STATES, why WOULD they delegate that sort of authority? Particularly when a number of the Original Thirteen had clauses in their ratification documents specifically RESERVING that power to themselves. As you well know, such having been posted here times without number! For Lincoln and FedGov to hold otherwise would legitimately be a violation of the contract they had with the States to be their agent in certain, VERY LIMITED matters. As the ratification documents were legally binding in setting up the Union, why ever would you think that the secession clauses should not be EQUALLY binding?
It's implied. At least James Madison believed so.
Particularly when a number of the Original Thirteen had clauses in their ratification documents specifically RESERVING that power to themselves.
So what? They also contained clauses saying that they ratified the Constitution as passed out of convention and agreed to be bound by its provisions. Their ratification documents don't supersede the Constitution, and if an act they claim they reserved to themselves is unconstitutional then it's unconstitutional.
As the ratification documents were legally binding in setting up the Union, why ever would you think that the secession clauses should not be EQUALLY binding?
Legally binding how?