Yes. I've read newspaper articles and various commentary from that time period, and they absolutely did not like the idea of New Orleans not being under their control.
Allowing the South to secede peacefully would have been a financial disaster for the North. It also would have effectively repealed Union tariffs because of the wide porous borders between the Confederacy and the Union, and the fact the Mississippi reaches so deeply into Northern states.
Secession would have undermined their Federal income schemes and disabled most of their protectionist laws.
It would have cost them big money in the North.
It is no accident that they concentrated so much effort on taking Vicksburg and New Orleans in the war.
Correct.
"Down here they think they are going to have fine times. New Orleans a free port, whereby she can import Goods without limit or duties, and Sell to the up River Countries. But Boston, New York, Philadelphia and Baltimore will never consent that N. Orleans should be a Free Port, and they Subject to Duties." William T. Sherman
The predicament in which both the government and the commerce of the country are placed, through the non-enforcement of our revenue laws, is now thoroughly understood the world over....If the manufacturer at Manchester (England) can send his goods into the Western States through New Orleans at less cost than through New York, he is a fool for not availing himself of his advantage....if the importations of the country are made through Southern ports, its exports will go through the same channel. The produce of the West, instead of coming to our own port by millions of tons to be transported abroad by the same ships through which we received our importations, will seek other routes and other outlets. With the loss of our foreign trade, what is to become of our public works, conducted at the cost of many hundred millions of dollars, to turn into our harbor the products of the interior? They share in the common ruin. So do our manufacturers. Once at New Orleans, goods may be distributed over the whole country duty free. The process is perfectly simple. The commercial bearing of the question has acted upon the North. We now see whither our tending, and the policy we must adopt. With us it is no longer an abstract question of Constitutional construction, or of the reserved or delegated power of the State or Federal Government, but of material existence and moral position both at home and abroad. We were divided and confused till our pockets were touched." New York Times March 30, 1861
March 18, 1861, the Boston Transcript wrote: If the Southern Confederation is allowed to carry out a policy by which only a nominal duty is laid upon the 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 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 all its obligations, if this state of things were not provided against.
[the North relied on money from tariffs] “so even if the Southern states be allowed to depart in peace, the first question will be revenue. Now if the South have free trade, how can you collect revenues in eastern cities? Freight from New Orleans, to St. Louis, Chicago, Louisville, Cincinnati and even Pittsburgh, would be about the same as by rail from New York and imported at New Orleans having no duties to pay, would undersell the East if they had to pay duties. Therefore if the South make good their confederation and their plan, The Northern Confederacy must do likewise or blockade. Then comes the question of foreign nations. So look on it in any view, I see no result but war and consequent change in the form of government. William Tecumseh Sherman in a letter to his brother Senator John Sherman 1861.