The people of the time would greatly disagree:
3/18/1861 It took only a week for Northern newspapers to understand the meaning of the low Confederate Tariff announced the week earlier in Montgomery.
The Boston Transcript wrote,
“It does not require extraordinary sagacity to perceive that trade is perhaps the controlling motive operating to prevent the return of the seceding States to the Union.
“Alleged grievances in regard to slavery were originally the causes for the separation of the cotton States; but it is apparent that the people of the principal seceding states are now for commercial independence. They dream that the centers of traffic can be changed from Northern to Southern ports.
“The merchants of New Orleans, Charleston, and Savannah are possessed with the idea that New York, Boston, and Philadelphia may be shorn, in the future, of their mercantile greatness, by a revenue system verging upon free trade.
“If the Southern Confederation is allowed to carry out a policy by which only a nominal duty is laid upon imports, no doubt the business of the chief Northern cities will be seriously injured thereby…
“The difference is so great between the tariff of the Union and that of the Confederated States, that the entire Northwest must find it to their advantage to purchase their imported goods at New Orleans rather than at New York. In addition to this, the manufacturing interest of the country will suffer from the increased importations resulting from low duties.“
“The government would be false to its obligations if this state of things were not provided against.”
This problem prompted numerous politicians and businessmen to rush to Lincoln to advise him to invade the South.
But the fears expressed in the editorial makes no sense. Leaving aside for the moment the question of how goods bought in New Orleans would reach the Northwest, if they did buy their goods from New Orleans in the now independent Confederacy then wouldn't the U.S. tariff still be applied the moment they were landed in a U.S. port? And if the Confederacy levied their tariff first then U.S. consumers would be paying more for goods delivered that way.
Would U.S. shipping be impacted by the separation? Perhaps, especially if the split was acrimonious. Coastal shipping might take a hit under those circumstances. But there is no reason to believe that the traffic into and out of Northern ports would dry up. Exports of Southern cotton would still leave from Southern ports, and if the separation was peaceful then there is no reason to believe the some of that wouldn't continue to be carried in U.S. ships.
Yup. A war to cover up their impending loss of money.