"We have been through it, and it made no more sense the second time around than it did the first. The idea of a tariff-free south posing a threat to the North is ludicrous."The point is not so much whether it makes sense or not. The point is how it was perceived in the North. I did, you will notice, refer to perception, but I am by no means so certain as you that the perception was unrealistic. As to the reality of the perception, there are many editorials from Northern newspapers, and they have been repeatedly posted on these threads, in which the writers predictored extremely dire consequences for the Northern economy. There can be no doubt that they played a major role in winning popular support for the suppression of secession. They occurred around the same time as the firing on Fort Sumter, so the effects of the two can't be easily disentangled.
There were a whole raft of editorial proclaiming gloom and doom with the rebellion of the southern states. There are currently a whole series of editorials proclaiming gloom and doom over the policies of George W. Bush. That doesn't make either one of them right. I don't see where the south posed a threat to the North from an economic standpoint. Every item imported into the U.S. that had a tariff levied on it would have paid that tariff regardless of where they crossed the border. All shipping through the south would have done is increase the costs, not decrease them.