The very first item on the list of causes for each and every state listed there was the protection of their right to maintain slavery.
How could any one say that the south seceded for every other reason but slavery?
Well, since they likely equated that with thier right to property, it would seem "valid" on it's face.
How could any one say that the south seceded for every other reason but slavery?
Some may. I dont.
Disclaimer: Because some people are so obtuse - my first statement above does NOT mean I agree with the reasoning - instead the argument itself would have been one that could be argued according to the laws and customs of the time.