[DiogenesLamp]

First notice DiogenesLamp here wishes to draw our attention away from not just "slavery, slavery, slavery" but also "tariffs, tariffs, tariffs", towards what?

The real issue. The money from European trade that would be lost if the South began direct trade with Europe. It is the reason the North had to stop them. If they did not, there was about to be a major power shift to the South.

[BroJoeK]

DiogenesLamp on what caused secession: "The real issue.
The money from European trade that would be lost if the South began direct trade with Europe.
It is the reason the North had to stop them.
If they did not, there was about to be a major power shift to the South."

And yet that was not the main reason for secession expressed by anyone in late 1860 & early 1861.
Yes, both Rhett and Stephens mentioned trade, briefly, but not in your sense here and certainly not to imply trade was the "real reason" for secession as opposed to slavery.

Some Northerners did worry about trade, mostly Democrats and their first thought was to join the new Confederacy.
They are the ones Robert Toombs referred to in advising Jefferson Davis against military assault on Fort Sumter:

""Mr. President, at this time it is suicide, murder, and will lose us every friend at the North.
You will wantonly strike a hornet's nest which extends from mountain to ocean, and legions now quiet will swarm out and sting us to death.
It is unnecessary; it puts us in the wrong; it is fatal."[15]"

Republicans were more concerned about the basics -- Constitution, Federal properties, Confederate declaration of war on the United States, etc.
Consequences of changes to trade patterns were less immediate in Republican minds.