Uh, this wasn't my own deduction. This deduction came from Paul Craig Roberts. Also, this does not ignore what they actually said. It very strongly incorporates what they actually said as the supporting evidence for the entire premise.
Paul Craig Roberts, who wrote the article, also comes very close to being a Holocaust denier. He's not to be trusted.
I think i've heard of him before, but I can't recall reading anything else that he's ever wrote. He's not like Victor Davis Hanson, or Ann Coulter, or Kurt Schlichter, or any other famous writer on the right.
So you didn't find his explanation interesting or relevant? Okay then.
His theory is that what they said wasn't what they really meant. So for Roberts, what they said is hardly "supporting evidence for the entire premise." On the contrary, the evidence is something he ignores because it doesn't fit with his cockamamie wackadoodle theory.
If they didn't want tariffs, they could have stayed in Congress and modified them. The actual evidence is that they very much cared about other things - not the tariff.
Another stupid thing about the theory - proclaiming the rightness and goodness of slavery cost the secessionists much support abroad and closer to home.
Making that declaration wasn't something they benefited from. It was something they wouldn't do if they didn't have to do it. And the tariff wasn't a strong enough reason to run the risks that making slavery their cause would make for them.