On economic causes of civil war
Paul Collier and Anke Hoeffler
the Yankees were for the most part fighting not to abolish slavery, but for their economic interests...the tariff became the single most important domestic economic issue prior to the Civil”
http://www.amazon.com/Understanding-Civil-War-Evidence-1-Africa/dp/0821360477
Slavery brought bad juju on all territories that permitted it.
I suppose it could be an economic interest not to have someone declare war on you.
In fact, a Google search of that line reveals that the first part comes from "Tariffs, Blockades, and Inflation: The Economics of the Civil War" by Robert Ekelund and Mark Thornton and that the second part, after the ellipse, is a version of a line 14 pages earlier in the book.
Sorting out your sloppy historiography, it appears that what you did was pick up a review of the Ekelund and Thornton book by Tommy DiLorenzo, who himself messes up the quote about tariffs (not the first time for him to do that), and then you compound your error by mistaking DiLorenzo's citation of Collier and Hoeffler's work in another context with being the source of the botched quote.
WIth that sort of sloppiness, it's no wonder you get so much wrong.