It would have economically destroyed the powerful men that were backing Lincoln. Northern shipping, manufacturing, banking, insurance, warehousing, and countless other industries would have been badly damaged by direct trade between the South and Europe.
It wasn't about the 65 million or so in Federal revenue. It was about hundreds of millions of dollars lost to Lincoln's wealthy backers in the North East.
I believe you are absolutely correct. Have you read this from 1860?
"By mere supineness, the people of the South have permitted the Yankees to monopolize the carrying trade, with its immense profits. We have yielded to them the manufacturing business, in all its departments, without an effort, until recently, to become manufacturers ourselves. We have acquiesced in the claims of the North to do all the importing, and most of the exporting business, for the whole Union. Thus, the North has been aggrandised, in a most astonishing degree, at the expense of the South. It is no wonder that their villages have grown into magnificent cities. It is not strange that they have"merchant princes," dwelling in gorgeous palaces and reveling in luxuries transcending the luxurious appliances of the East! How could it be otherwise? New York city, like a mighty queen of commerce, sits proudly upon her island throne, sparkling in jewels and waving an undisputed commercial scepter over the South. By means of her railways and navigable streams, she sends out her long arms to the extreme South; and, with an avidity rarely equaled, grasps our gains and transfers them to herself—taxing us at every step—and depleting us as extensively as possible without actually destroying us."
[Vicksburg Daily Whig, January 18, 1860, quoted in Dummond, Southern Editorials on Secession, in Kenneth M. Stampp, "The Causes of the Civil War." 1986, pp.65-66]
I have that book by Dummond, and the Vicksburg article is over 1,150 words, with a theme centered around the thought, "Why did we let the Yanks take advantage of us like this? Why have we not been manufacturing our own cloth?", and etc..
Mr. Kalamata