They just wanted to own people dammit!

Well pull out the constitution of the CSA. It was mostly copy and pasted from the US constitution with a few minor changes (single term president with line item veto power). It did nothing to stop the power of their federal government. The Supremacy, Necessary and Proper, or Interstate Commerce Clauses. You know, the stuff that actually restricts "State's Rights."

Then, the CSA constitution even took away the rights of a state to regulate slavery within it's boundaries. On top of taking out the vague references to slavery and making "Negro Slavery" an explicitly protected institution. On top of that, it took away the right of states to determine their own electorate and their protections for free trade between states.

"State's Rights" is a post hoc justification and not even a good one.