The relevant point about the "Cornerstone Speech" is not whether Mr. Stephens spoke the exact words attributed to him or not. It is that these recorded words were widely distributed in southern newspapers and universally praised as the best possible statement of southern ideals and goals.
While softened by Christian sentiments, the ideology it expresses is essentially one of the white man as the master race. It flatly rejects the Declaration of Independence for being wrong when it asserts that "all men are created equal."
I have never seen any contemporary statement from Mr. Stephens in which he clarifies or denies any of the statements attributed to him in this famous (and very eloquent, if disgusting) speech.
As far as the "extension of slavery" goes, it is well known that many in the South viewed the Caribbean and Latin America as a future field for such expansion. As far as I know, the Confederate Constitution did not provide for the prohibition of slavery in any territory acquired in the future by the Confederacy.
That is correct. The ultimate goal of the Confederacy was the expansion of slavery empire and the overthrown the United States government in order to carry out their diabolical plans.
After all Confederates succeeded in murdering a U.S. President and would have murdered the entire Lincoln administration if the treasonous conspiracy had been totally implemented.
Such a cowardly assassination of a United States President, yet fanatical neo-confederate voice approval. How demented.