Why does Elliott refer to the "cornerstone speech" of Alexander H. Stephens in making his argument?

The "Cornerstone Speech" by Alexander Stephens is the usual bludgeon of choice. Stephens, a Georgian who had served in Congress, was the new vice president of the CSA in the spring of 1861, and in this speech he explained the new Confederate constitution and the prospects of the new nation, as he saw them, to an audience in Savannah. Here is how one commentator cherry-picks the usual cherries from it: Stephens's post-war writings downplayed the importance of slavery in the sectional conflict, and they formed much of the foundation of the first generation of defense of the Southern nation - - the so-called "Lost Cause" view of the war. That reasonably can be dismissed as a convenient revisionism.

:)