Here are a few more of Colwell’s quotes from his pamphlet that I “cherry picked” for you.
From pg 51:
“We regard African slavery as it now exists in the South, as justifiable on sound social, humane, and Christian considerations.”
From pg. 55:
It is quite certain that slavery in the South is not understood and appreciated in the North or in Europe as it should be...
“...an institution which so much concerns the interests and well being of human beings...deserves to be studied.
“...slavery deserves a social code of is own”
“...there are many large slaveholders in the South.....that if brought together for conference...might produce a constitution for slaves....after such a measure...abolitionism could no longer exist.”
I do not see or hear any rebuttal to Kettell’s economic study in any of that from his pamphlet.
I am not an economist either, but I know that you can't simply ignore the analytical parts of a book and then claim that it offers no analysis.
In a nutshell, Colwell argued:
The Five Cotton States are large importers of Northern commodities, many of which are made expressly for them; in payment for these, and for advances on cotton, they give not their surplus of cotton, but the chief part of their cotton, either in kind, or in Bills of Exchange drawn upon it, or Bills of Lading transferring the ownership of it.
Whether or not he proves that decisively, I can't tell, but he does bring forth information to support his contentions. If his statistics are less comprehensive than Kettell's, nonetheless he does offer analysis and argument and doesn't try to overwhelm the reader with reams of data of dubious relevance.
You are also shameless in ignoring the situation in 1860. Slavery was a fact. It had passionate defenders. It wasn't going away any time soon. Abolitionism was a crime in many states and a scandal to the rest of the country.
Anyone making an appeal to slaveowners or supporters of slavery or those who were neutral would have to accept the fact of slavery and indulge in some flattery or risk being condemned as an abolitionist.
Abolitionist literature was banned -- and often burned. That was the fate of Hinton Rowan Helper's The Impending Crisis of the South, a book which tried to make a very pro-Southern argument against slavery which was quickly banned, vilified, and burned.
I'm not saying Colwell was a secret abolitionist, just that -- given the circumstances -- you can't blame him for making flattering appeals to people who weren't outraged by slavery.
We hear over and over again that one can't judge 19th century figures by 20th or 21st century standards, yet here you are doing just exactly that.