You addressed your question to N-S, but I'll answer.
Your quotations are selective and therefore fallacious.
The full record shows that their concern was much more general than just the institution of slavery, which was a great concern (I disagree with some other Southerners on this) of course, since their economy rested on it as surely as Illinois's economy rested on the ability of families to run freehold farms.
Their threatened inability to sustain slavery meant that they would be unable to sustain anything under a regime that made entire regions of the country playthings of a faction. This was what Madison and Calhoun had both been concerned about -- and what Hamilton had been working for all along, until the day he was shot dead. It was the taking of the country into receivership by the industrial and business classes.
When the confederates had the opportunity to write a constitution for their bastard republic, what did they do? Pervert the Constitution of the United States by adding a bunch of explicit slavery protections.
In the United States Senate, did the southern senators permit the open discussion and debate on the issue of slavery? No, for decades they instituted gag rules.
Did the federal post offices allow the deleivery a mail and newspapers which carried abolitionist ideas? No, they censored that material.
Did the courts in the south uphold the right to free speech? No. They permitted no dissent.
From this pre-election (1860) Louisiana broadside:
"The slavery agitation will soon make the North and the South two separate nations, unless it can cease, of which we have little hope.... We can never submit to a Lincoln inauguration; the shades of revolutionary sires will rise up to shame us if we shall do that.... Let us drop all discussions and form a Union of the South." (from William C. Davis, Look Away, pg 26)
Open your mind, pequeño.