Did you even read the speech? I am forced to conclude that you did not in light of such a comment. Either that, or you have difficulty with your comprehension skills. Allow me to assist you though with a key excerpt from the speech:
"One of two things must be done: either you must prevent imports into those States, which I do not think you can do; and I do not suppose there is a Senator on this floor who believes that, under the existing laws, the President has authority to do it; or you must call Congress together, and invest him with some authority. If you do not do that, you must establish a line of custom houses on the border. Is it not better for us to meet this question frankly on its merits? My apprehension, as I have already expressed it, is that the Administration intend, (I hope I may be deceived) as soon as they can collect the force to have a war, to begin; and then call Congress suddenly together, and say, "The honor of the country is concerned; the flag is insulted. You must come up and vote men and money." That is, I suppose, to be its policy; not to call Congress together just now. There are two reasons, perhaps, for that. In the first place, it would be like a note of alarm down south; and, in the next place, if you call Congress together, and deliberately submit it to them whether they will go to war with the confederate States or not, I do not believe they would agree to do it. Of course, I do not know what is the temper of gentlemen on the other side; but, though they will have a large majority in the next Congress, I take it for granted from what little I have heard, that it will be difficult to get a bill through Congress for the war before the war begins; but it is a different thing after fighting begins at the forts."
As the speaker admits, the South was buying most of their European goods from Northern importers, so it was Northerners who were paying the vast majority of the import duties, not Southerners
You have just demonstrated your comprehension of market concepts falls short of even your reading ability. Tariffs are not paid by one intermediary in the economy then forgotten about. They are passed on to the consumer by way of the prices.
and the speaker's assumption that the Southerners could simply shift their importing to Southern ports is highly suspect, since it is apparent that importing European goods through Northeastern ports was much more cost efficient.
It is not suspect in the least. If a barrier to trade exists in the north (i.e. a high tariff) but not in the south, the goods will go to the place where they can achieve entry, meaning the south. It's a simple matter of economic law, and also one that the otherwise economically incompetant yankees even understood. The New York Times even urged war on these grounds, noting that their high tariff would drive away trade, and the south's low tariff would pick it up. The New York Herald noted the same to be true. And sure enough, the Morrill bill virtually killed off trade with Europe after it was enacted.
Moreover, even if you assume that the speaker's numbers are correct that Southerners were buying $220 million worth of imports annually and thereby indirectly paying as much as $30 million annually in import duties, that would still be a mere pittance in comparison to the Republican threat to slaveholding
Not when you consider that those figures were from the 1857 tariff, which was low and favorable to free trade. The grievance was with the Morrill act, which practically destroyed international trade with Europe. The southern economy was almost entirely export-based, and when trade halts so do exports.
What is it about that quote that leads you to believe that "tariffs" played any significant role in secession or the Civil War?
You have just demonstrated your comprehension of market concepts falls short of even your reading ability. Tariffs are not paid by one intermediary in the economy then forgotten about. They are passed on to the consumer by way of the prices.
Not necessarily. The importer who pays the duties may not be able to sell his imported goods at all (or may be forced to discount them) if domestic goods are available at a lower price, and in fact that was the main reason (albeit not a sound one economically) for Congressional passage of the high import duties.
If a barrier to trade exists in the north (i.e. a high tariff) but not in the south, the goods will go to the place where they can achieve entry, meaning the south.
You're begging the question by asserting that the "tariff" was a "barrier" to trade (as opposed to merely a relatively small burden on imports).
the Morrill bill virtually killed off trade with Europe after it was enacted.
That isn't true, but discouraging imports was certainly the intent of the bill. It was an unwise protectionist measure, but it played no substantial role in secession or the Civil War.
The grievance was with the Morrill act, which practically destroyed international trade with Europe. The southern economy was almost entirely export-based, and when trade halts so do exports.
That's total nonsense. The secessionists' grievance (by their own emphatic admissions) was the threat posed to slavery by Lincoln and the Republicans. Most of the Southern states seceded before the Morrill tariff was passed, and the rest seceded as a result of Lincoln's refusal to permit the Confederates to steal federal property (i.e. Fort Sumter). What destroyed the South's economy was basing it almost entirely on slavery.
Moreover, there was no tax on exports, so even a high import duty would not stop Southern cotton from being exported to Europe (just as Japan's high import duties never stopped Americans from buying Toyotas and other Japanese goods).
The "Morrill tariff" raised import duties from an average of 19% to 33% (source), so even using Senator Clingman's highest estimate, that would only raise the South's annual import tax burden from $30 million to $51 million, still far far less than the value they placed on slavery. They claimed that the slaves they held in bondage were worth $3 billion to them (which in today's dollars would amount to about $100,000 per family). The social value they put on keeping negroes at the bottom rung of society apparently far exceeded that, since the Confederate citizenry were willing to give up hundreds of thousands of their sons to try to hold onto their "peculiar institution".