As I believe you pointed out in a previous post, the theory that the war was about tariffs was floated after the war to obscure the fact that the root cause was slavery. Thus the losers could claim they had not fought for slavery.
What I find truly bizarre is that just about every national institution in the country broke apart in the two decades before 1860, including every religious denomination except the Catholics. In each case, the proximate cause was disputes over slavery. Finally, in 1860 the political parties broke over the same issue, which resulted in Lincoln's election.
Yet when the southern states seceded, breaking apart the nation itself, that somehow was unrelated to the issue that had broken every other institution.
Very strange logic there.
Another thing I find odd about The-South-Will-Rise-Again boys is their taking present day attitudes and institutions and projecting them into the past. They speak of (in 1860!) an overwhelmingly powerful federal government, or of irresistible presidential power.
In 1860, by today's standards, the federal government was barely there. Lincoln could not lead an unwilling Union into war to prevent secession. He didn't have the mechanisms to do any such thing. The vast majority of Union soldiers were volunteers, and without support from Union states the federal government could have done little, especially in the first year or so.