You're the one insisting that it was ONLY slavery, remember?
My position is that this really pissed them off. You seem to deny this for some reason.
"The Congress shall have power – To lay and collect taxes, duties, imposts, and excises for revenue, necessary to pay the debts, provide for the common defense, and carry on the Government of the Confederate States; but no bounties shall be granted from the Treasury; nor shall any duties or taxes on importations from foreign nations be laid to promote or foster any branch of industry; and all duties, imposts, and excises shall be uniform throughout the Confederate States"
Protectionist tariffs pissed them off to such an extent their Constitution expressly forbade such favoritism.
Time to acknowledge, "Yes, they said slavery, but at the end of the day the Union wasn't a good deal for them."
They said that too.