"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."You just don't seem to get the point; perception is what mattered, not the accuracy of the prediction. The Dow plummeted, at least partially due to the Bush editorials, so, perception matters.
"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."
But no U.S. tariff would have been collected on goods shipped to and sold in the Confederacy.
"All shipping through the south would have done is increase the costs, not decrease them."
On goods sold in the North? Of course, you are absolutely right, that is precisely the point.
No tariff was collected on goods from the North shipped to and sold in the south prior to the rebellion, either. Items manufactured in the North could still have been exported to south so the market remained. They may have had to adjust prices to keep their markets, but they could still have undercut European manufactureres. Since the overwhelming majority of imports already came in through Northern ports then tariff income would have continued and the government funded. It would have been the south faced with the problem of funding their new government and their huge army. They would have had little choice but to have turned to a tax of some sort, probably a tariff of their own.