Let me just clarify my point--constitional may not even be the best term for it. The key point for me would be that all states were in attendance, and all states would agree to a set of rules. But then, I go around in circles, because the states already have such a body--it's called Congress. And they have two different means of amending the Constitution. And the Scotus. Failing all of that, in extreme cases, Madison would admit the right of the states to preserve their rights.
But there we fall into that question of what is extreme and what isn't. There's no clear definition of that. IMO, the slave states fail on all counts. Heck, they had their way in Congress all the way back to 1787. They were clearly willing to secede over actions that were constitutional. Like a Presidential election. No convention would cure that. However, if they wanted to leave the Union, to me, you could have at least held some sort of convention, where all the parties are present and agree to the rules.
Again, that seems absurd, given the Congress and the other departments in existence for the purpose of collective agreement.
Agreed. It does seem that the actions of Congress would indicate the results of any convention involving all the states; perhaps that's the reason why none was called for. While certain perceived abuses by the national government would allow for recourse through the courts, questioning the tarrif power (one example) is not one of them.
Given that a nationally representative body had already weighed in on that issue, it doesn't seem unreasonable that the South would have to then appeal to the next logical means of asserting their rights.