You misunderstand me, slavery WAS a part of the issue. Taking away the major source of labor for one entire half of the country, would be a catastrophe, so the South had a reason to be upset. However, it came down as a part of the larger issue of State's Rights....
I am not saying slavery was the only issue. I am not saying that necessarily most southern men enlisted to fight for slavery, or at least not solely (One Virgina private to his Union captors: "I'm fightin' because you're down here."). I am saying that the break could not have happened without slavery. It was in the end the one issue that could not be compromised. And to the extent that economic causes were in play, they were mainly so because they were rooted in slavery, the foundation (as you concede) for the southrn economy.
I think in the hullabaloo to reestablish a real federalism, some folks get so worked up by the taint of states rights with the Confederacy or Jim Crow that they work too hard to try to establish that slavery really was not a major factor in thwe Civil War. And I just doen't see how any fair reading of history can support that idea.