Total rubbish, an absolute lie...
First of all, tariffs were only on imports, and since there were no imports of Southern agricultural products (i.e., cotton, tobacco), there was nothing for Federal government to protect against.
And in fact, those import tariffs in 1860 were as low as ever -- less than half of the "Tariff of Abominations" (35%) passed by Tennessean Andrew Jackson's supporters and South Carolinian Vice President Calhoun in 1828, reduced only slightly by President Jackson in 1832.
Point is: tariffs were standard "politics as usual" in our young republic, they went up, they went down, and in 1860 were the same rate (15%) as in 1792 under Founding President George Washington.
So tariffs were in no-way, shape or form the cause of Deep South declarations of secession.
The real cause was slavery, as secessionists officially explained, for example, here.
There has been a great deal of flurry in business circles in this city for a few days past, sending off goods to the South purchased before the 1st of March, on which day the new tariff takes effect. The Congress of the Confederated States have adopted a tariff similar to the United States, imposing the same duties on goods coming from the Northern States as we now pay on those imported from Europe. South Carolina wanted to establish free trade, but she could not have her way in that respect; so that in the future the products and manufactures of the North will have to enter the Southern market subject to the same impost as foreign goods. The new tariff adopted by the Congress at Washington [rb note: the Morrill tariff], if it should become law – which it will unless Mr. Buchanan keeps it in his breeches pocket – will surround our commerce with Europe with so many obstructions and difficulties that in conjunction with the disadvantages of the Southern tariff, New York will receive a blow more severe than any it has experienced within fifty years.
The trade of the Southern States, and of the cotton States especially, is of more importance to New York, and indirectly to Boston and Philadelphia also, than the whole trade of the West put together. And for the reason that it is more safe and reliable; because the Southern planter has a fixed locality and a certain property; he has his plantations and his negroes; he is always to be found, and he has on the spot a security for his indebtedness. Hence his pay is always prompt. But in the Northwest, on the other hand, society is like a quicksand; it is continually shifting and changing, rising and falling. There is nothing persistent about it. Its ability to pay is dependent on uncertain crops; there is very little money there; and it is extremely difficult to collect accounts in that section, as many of our merchants know.
The effect of these two tariffs, then, upon our trade with the best, and most reliable part of the country will most disastrously be felt in all the Northern cities. We learn that even now some of the largest houses in the Southern trade in this city, who have not already failed, are preparing to wind up their affairs and abandon business entirely. The result of this as regards the value of property, rents, and real estate, can be readily seen. Within two months from this time it will probably be depreciated from twenty to forty percent.