“Abraham Lincoln, one of the great scholars of the Declaration of Independence, knew the distinction well. The south separated not for the principles of liberty but for slavery...”
Abraham Lincoln was not a “scholar” of the Declaration of Independence, although I am sure that he actually read it more than a few times.
The South did wish independence for Liberty, and to preserve their distinctive culture. It sounds paradoxical in view of the slavery issue, but if you read what Southerners said, and look at their actions, it is evident. The North, on the other hand, was outraged that the nation was being weakened by division, and saw secession as unpatriotic and treasonable. You can fairly say that the motives on both sides were very similar.
I have a letter from an ancient cousin who fought in the Union Army from Pennsylvania. He feared that the South would invade and destroy his state! A Virginian might almost have written the same letter.
When it came down to slavery or independence, independence was more important to the leaders of the South. That is why they instituted a plan (too late!) to arm slaves as soldiers, and to give them freedom in return for service to the Confederacy. Many Southern leaders were not favorable to slavery, including Lee. That is why when the war ended, amongst the destruction and defeat, the South felt one sense of relief: that the slavery matter was over with. Almost no one wrote anything advocating its return, ever. I think that they were glad to be done with it.
I have read what Southerners wrote. Here are links to two secession authoritative documents:
Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union
http://www.yale.edu/lawweb/avalon/csa/scarsec.htm
Georgia Secession
http://www.yale.edu/lawweb/avalon/csa/geosec.htm
Both explicitly state that the issues of slavery caused secession.