I think what trips people up is a conflation of chief concerns; they assume that if Tom DeLorenzo’s argument that slavery was not Lincoln’s (and the Republican’s) chief concern, then the South must have been acting in response to the things that were Lincoln’s (and the Republican’s) chief concerns.
But the future of slavery was among Lincoln’s, and certainly the electoral base of the Republican Party’s concerns, and so the Deep South states acted primarily (though not exclusively) in response to what they thought Lincoln’s election indicated.
This does not mean they weren’t also concerned with the Republican Party’s position on, say, tariffs; and certainly the Republican Party’s position on slavery had implications for state sovereignty generally; but it is extremely (extremely) unlikely they would have seceded had they not felt the ‘peculiar institution’ was directly threatened by the election of Lincoln.
In other words, Tom DiLorenzo can be correct without it at all suggesting that the Deep South’s secessions were not motivated chiefly by slavery. This is why the position of people like him and Tom Woods has always been whether it was strictly required to engage in a massively destructive war that killed over 800,000 people and destroyed Federalism in order to get rid of slavery (especially since that wasn’t necessarily the topmost concern of the people waging the war), given that it was eliminated in all other countries without such slaughter and devastation. Even an independent Confederacy would have had to eliminate it sooner or later – and who knows – it is hard to make counterfactuals – but while in such a case it is hard to imagine the freed slaves facing no discrimination after the end of slavery, perhaps there would have been no Black Codes, Jim Crow, “Separate but Equal,” and the like. Again, in few other countries were the status of freed slaves entirely equal, but their situation wasn’t as bad, and part of how bad it became can partly be attributed to counter-reaction to how the end of slavery was felt to be forced violently upon the south through the war & reconstruction. (Note to point this out is not at all to excuse it, and I’m certainly not claiming “all would have been daffodils and magnolias and the brotherhood & sisterhood of all humanity in the South, it would have become a land of egalitarian fellowship of equality under law by 1870 if it wasn’t for that darn Lincoln fellow and his Radical Republican brethren messing with the natural evolution of things”).
(Feel free to correct me if this is wrong).