“Whether we remain in one confederacy, or form into Atlantic and Mississippi confederacies, I believe not very important to the happiness of either part. Those of the Western confederacy will be as much our children & descendants as those of the Eastern.” He wrote that if those of the Mississippi valley should “see their interest in separation, why should we take side with our Atlantic rather than our Mississippi descendants? It is the elder and the younger son differing. God bless them both, & keep them in Union, if it be for their good, but separate them, if it be better.” -—Thomas Jefferson
Thomas Jefferson’s comment was made knowing a state or states may secede from the United States of America by and only by exactly the same means by which they acceded to the United States of America as set forth in the Articles of Confederation and the Constitution that said the alteration to the perpetual union “be agreed to in a congress of the united States, and be afterwards confirmed by the legislatures of every State” and not “without the consent of the legislatures of the states concerned as well as of the Congress.”
The leadership of the Confederate States of America knew full well the means by which they attempted to secede their states from the perpetual union of the United States of America were unconstitutional and liable for punishment as treason, but they did so anyway in the firm conviction there was virtually no chance whatsoever they could secure the consent of Congress or the necessary ratification by the other states of the United States of America for secession of their own states. They were so certain of their inability to secure popular consent for secession, they often refused to permit a popular vote on the proposition and intimidated, arrested, and murdered delegates who refused to vote for secession. Everytime the people or their delegates rejected the proposition for secession, the rules were changed to deny the opponents the opportunity to reject the proposition for secession in the next attempt to pretend a popular referendum had been conducted for secession. Consequently, the acts of secession which potentially could have been attempted lawfully were instead conducted unlawfully and often by force of arms and intimidation of the citizens opposed to the unlawful acts.
The methods of secession are irrelevant. The fact that one or more of the Founders did not oppose secession IS relevant.