Sure there is. You simply do not wish to allow for the presence of that knowledge among participants in the politics of that time. Free trade was thought highly of among Southerners and its theory was developed in their political thinking. In addition the economic basis for free trade developed by Ricardo had been around for almost half a century and the practice of a free trade system had been policy for some time.
There is the one mathematical answer that can be applied to all conditions.
No, not really. There are basic rules of economic behavior out there though, and their validity may be shown graphically though. The Laffer curve, for example, is one of them. Another is a tariff's implications for an economy.
The protectionist argument was that on the whole the development of industry through tariffs would benefit the country in the end.
Yes. You've said that. It does not make it a valid argument though, and the laws of economics show that it is far from valid. Industry develops into areas of advantage and comparative advantage on its own under free trade conditions. Tariffs serve to impede that and artificially distort the economy into something that it is not and cannot sustain fully. Now, protection for INFANT industry is permissable and beneficial to a degree, but that is not what the protectionists of 1860 wanted. They wanted indefinate continued protection of their personal resources by eliminating the foreign competition with tariffs.
Condemn protectionism morally and one can't avoid condemning the greater offense of slavery.
Who ever said slavery was not condemnable? My point is that shouting "but...but...but...the south had slaves!" is simply not an answer or excuse to the intrinsically immoral act of using the government to make yourself fat to the detriment of everybody else. You have yet to address that issue and instead only respond with a tu quoque variation of shouting slavery. You are peddling a non-answer by attempting to excuse and obscure the protectionist's sins by addressing it only as a matter of relativity to the sin of slavery. That simply will not fly.
I have raised a number of points that you have not addressed -- Confederate support for sugar tariffs
You have obviously neglected to read my responses then as I addressed that point specifically. Condemnable as they may be, the small minority of southerners who benefited from the sugar tariff in no way makes the entire south into tariff lovers. One could just as easily say there were old whig southerners who favored tariffs, which is true in itself, but just as pertanent to that argument is the fact that they were a small minority of the southern population. Any population is bound to have minority political opinions within it. That does not mean that minority opinion is somehow on par with or overriding to the majority opinion.
the role of protectionists in promoting an industrial capitalist economy
The practice of business sleeping with government is not true capitalism.
Economists were far more divided on free trade and protection than they are now. It was still a living question, not a settled matter or fixed dogma. And the very association of free trade with plantation slavery, drove many who desired freedom towards protection as an alternative. I don't fault them for making that decision.
The prominence of economists among today's Confederate apologists is striking. They confidently insist that they have the answers, but they aren't always asking the same questions that people asked then or considering the state of knowledge at the time. The devotion of 21st century economists to 19th century slaveholders would be quite comic if it weren't so chilling.
As I've said, our approaches are so much at odds that there's no point in continuing. We aren't asking the same questions. If anyone's been following the discussion this far and wants to continue, Gabor Boritt's book "Lincoln and the Economics of the American Dream" looks worth reading.