Well, no, it’s not in the least misleading. As you state yourself, throughout 1860 the tariff was indeed 15%, the same it had been in G. Washington’s day. That a higher tariff passed in 1861 as the direct result of southern congressmen leaving due to secession doesn’t invalidate my point at all.
More critically, I think you are getting a free ride by claiming that tariff rates justify secession and war. Absolutely nobody made this claim in 1860, since they openly and proudly proclaimed that the purpose of secession was to protect the institution of slavery.
By the end of the war, it was no longer possible to even try to justify secession in defense of slavery, so another “reason” had to be found.
Look, here, under the cushions! It’s the tariff we’d all forgotten about! That’s why we seceded! That’s the ticket!
Yet this in itself makes the unexamined claim that if tariff rates were indeed raised, secesssion and therefore by implication war or at least the risk of war would have been fully justified.
Really? Does any tariff rate really justify such extreme action? If killing 600,000 to 750,000 men isn’t justified by defense (or abolition) of slavery, we are somehow supposed to agree that killing them over a tariff rate is right and proper?
On December 12, 1860, before any state seceded, Texas Senator Louis Wigfall projected what the future vote counts would be on contentious issues. Before the new Congress convened Southern senators had the votes to stop the Morrill Tariff from being approved by the Senate as they had done earlier in that Congress. On the other hand, once the new Congress convened, Wigfall's vote projections indicated that the new makeup of Congress would pass the Morrill Tariff. The Morrill Tariff had already passed the House earlier in 1860. The country was going to get the impending Morrill Tariff whether Southern senators stayed for the rest of the outgoing session or not.
From an old post by GOPcapitalist quoting Wigfall on December 12, 1860 [Link]:
Tell me not that we have got the legislative department of this Government, for I say we have not. As to this body, where do we stand? Why, sir, there are now eighteen non-slaveholding States. In a few weeks we shall have the nineteenth, for Kansas will be brought in. Then arithmetic which settles our position is simple and easy. Thirty-eight northern Senators you will have upon this floor. We shall have thirty to your thirty-eight. After the 4th of March, the Senator from California, the Senator from Indiana, the Senator from New Jersey, and the Senator from Minnesota will be here. That reduces the northern phalanx to thirty-four...There are four of the northern Senators upon whom we can rely, whom we know to be friends, whom we have trusted in our days of trial heretofore, and in whom, as Constitution-loving men, we will trust. Then we stand thirty-four to thirty-four, and your Black Republican Vice President to give the casting vote. Mr. Lincoln can make his own nominations with perfect security that they will be confirmed by this body, even if every slaveholding State should remain in the Union, which, thank God, they will not do.
Your canard and straw man argument attempt failed.
You said: "By the end of the war, it was no longer possible to even try to justify secession in defense of slavery, so another “reason” had to be found."
Northern historians, politicians, and apologists could not justify the degree of carnage resulting from Lincoln's initiation of hostilities for the protection of the Union financial system.
For a century and a half they have had to resort to using the issue of slavery to rationalize the destruction of human life and failure of the Republican party and Congress to hold Lincoln responsible for his despotic actions."