The so-called "state's rights" is code for the right to own slaves.Unfortunately, to some people it was/is.
However, don't throw the baby out with the bath water. As you know, states rights is an approach set up in the Bill of Rights to limit the power of the central government.
When the central government tries to impose its laws on states and individuals in areas that are the purview of the states, then states rights can be used to stop it. Consider federal laws on the possession of guns near schools. It is not a federal issue, so the courts threw it out. "Under the theories that the Government presents...we are hard pressed to posit any activity by an individual that Congress is without power to regulate."
On the other hand, if you want an all powerful central government, then states rights is an obstacle that has to be overcome and demonized.
I agree with you that "state's rights" in the context of federalism is honorable and worthwhile.
However, I grew up in the Deep South during the era of segregation, and was taught romantic lies about "the War of Northern Aggression" and all that. And it just plain irritates me now.
I am eligible to join the Daughters of the Confederacy based on several ancestors, but have zero desire to do so as long as they spread lies.
Why not just tell the truth? Slavery was important to the Southern economy. Making the South give up slaves was as destructive as it would be to us if we had to give up gasoline. I had ancestors who owned slaves. I am not ashamed of it nor proud of it. It's a fact.
Further, by counting slaves as 3/5 of a person for purposes of the census, the South had representation in Congress disproportunate to their voting power. A slave owner who owned 100 slaves effectively had the voting power of 60 men. Spreading slavery to the western territories was a way of keeping that power.
The Civil War was about money and power, preserving an economic way of life. Nothing more, nothing less.