One of the reasons the Civil War still resonates the way it does all these 150 years later is that things aren't as, forgive me, black and whilte as you present them.
If push came to shove, yes, I'd agree with you that the acts of the leaders of the Southern cause were treasonous. But it's not as clear-cut as "they shot at soldiers of the United States" The world and the country were very different places then and in particular loyalty to state often trumped loyalty to the federal government. Beyond the political theory, the federal government was a largely passive entity a long way away from most people; the federal government was an abstraction while people's knowledge of government was county and state. At that time, even the great battles between farmers, ranchers and the government did not intrude into people's lives because the part of the country where that's relevant was barely settled at the time. Famously, Robert E. Lee is said to have not been a secessionist yet when it came time to choose up sides, he felt his loyalty was to his state, not the federal government. I don't say that to prove right or wrong but to illustrate that the worldview of people of the time was far different than it is today. The reason that it's different today is, well, the civil war, which among other things established the primacy of the federal government. Or put another way, the primacy of the federal government was not so well established before the civil war.
In my favorite moment from Ken Burns'
The Civil War somebody observes that prior to the Civil War, the common grammatical construction was "the United States are;" it was only after the war that people adopted the current form of the "the United States is." To me that is a small thing that speaks volumes and volumes and really drives home the point. As does the fact that as you note, "Benedict Arnold" is a term of unqualified derision and yet the names of Robert E. Lee, Jefferson Davis and others are not, even beyond the South and even including some of the more despicably public and outrageous racists. That says something about the continuing ambiguity felt by many people, not just southerners.
For your immediate purpose, what I see is the way these subtleties fit into the "duality of the southern thing." Yes, the South is the home of "Lost Cause Nostalgia" yet it has historically been (and I believe still is) the breeding ground for a hugely disproportionate number of service men and women (that is, soldiers in the federal military). Some of that has to do w/ the location of many of the larger military bases in the south and the handing down of the military tradition through generations, but not nearly all of it. At least in popular culture, the South is considered one of the homes of "traditional American values" and "flag wavers," yet those are the same people who do glorify the "Lost Cause." Souhterners are believed to have more respect for authority and yet continue to honor the ultimate break from authority.
Nothing here contradicts your point but I think it shades it quite differently. It's not just that "the home of redneck racists also produces great art." It's that the South in particular is a cauldron of steaming contradictions that go to the very roots and heart of what it means to be American. The "duality of the Southern thing" is a great description because it covers all these contradictions and confusions, not just the obvious one.