We don't care what their reasons were. We only care about what the UNION reasons were because *THEY* were the ones that insisted on fighting this war. Defenders have no choice but to fight, it is only the aggressor's motives which matter.
You want to keep the topic focused on the South's reasons for leaving, because it is the only moral angle you have to work with. Once the discussion is properly focused on WHY DID THE NORTH STOP THEM FROM LEAVING, does it become apparent that the Union was in the wrong.
So let's reform the question. Why did the North stop them from leaving? By what moral pretext did the North have the right to force them back into a government of which they no longer wished to be a part?
And how is it different from what England attempted to do?
But of course, it was the Confederacy which first provoked war, dozens of times, then started war at Fort Sumter, then formally declared war on the United States (May 6, 1861), then sent military aid to pro-Confederates in Union Missouri, then raised up an additional 400,000 troops (on top of their original 100,000) and ordered military supplies from abroad.
The Union merely responded to these Confederate acts of war by defeating them, unconditionally.
DiogenesLamp: "So let's reform the question.
Why did the North stop them from leaving?
By what moral pretext did the North have the right to force them back into a government of which they no longer wished to be a part? "
But of course, FRiend, you well know, the Union did nothing to stop secessionists from declaring their departure and forming a new Confederacy.
Neither outgoing doughface Democrat President Buchanan nor incoming "Black Republican" President Lincoln lifted a finger to stop the Fire-Eater secessionists.
War only began after the Confederacy provoked, started, declared and made war against the United States.
DiogenesLamp: "And how is it different from what England attempted to do?"
Just like Confederates in 1861 the Brits in 1775 abolished their old Massachusetts Bay compact, formally declared war on the colonies, and began to seize military supplies & property which didn't belong to them.
Only many months after Brits declared & started war against colonists did Americans finally declare their independence (July 4, 1776).
That's why I've always argued that if you wish to compare our Founders to Confederates, then Confederates must play the role of 1775 Brits, and our Founders that of the 1861 Union.
In short: 1861 Confederate assault to seize Fort Sumter equates to the 1775 British march to seize American arms at Lexington & Concord.