Good discussion. I find little to quibble with in what you have said thus far....but there are two points or questions I want to raise: one regarding the quoted statement above on Jefferson, the other on how could so many poor non-slave owners be motivated to fight for the rich man to own slaves.
I've done a 180 on my view of the Civil War. I come from a long line of Lee's in South Carolina dating back to the pre-Revolutionary War era. My my great great (etc) Grandfather fought in the Revolutionary War to help start what would become the USA, and his grandson serval decades later fought in the Civil War to help tear it all apart. To the best of my knowledge, none of my lineage owned any slaves. As I understand it, only the wealthy owned slaves; and the Lee's of this era were poor farmers. Reading the Confederate Constitution, there is no denying the South's stance and their post war ambitions with regard slavery. They wanted slaves and wanted it enshrined in the Constitution. One thing I still have trouble with, however, is what made poor farmers from the south want to march a 1,000+ miles, often times barefoot, in the snow and near starvation, just so some rich man could have slaves? Besides the obvious hardship, wouldn't that also be working against the self-interest of the poor farmer, as the wealthy slave owner would only persevere or strengthen their competitive labor advantage if slavery were to be persevered?
On Jefferson, I think the case against him raping and fathering a child with one of his young teenage slaves, Sally Hemmings, is grossly overstated. DNA evidence indeed confirms a Jefferson male fathered a child with Sally Hemmings--but not that it was not necessarily Thomas. Circumstantial evidence points to his brother as the more likely father given his propensity to frequent the slave quarters and general fondness for the African people. There is also ample speculation that Thomas Jefferson was not even in the country when Sally was impregnated. Of course, I can't in good faith bring this up without acknowledging that the Jefferson Foundation itself has fully surrendered to the theory that Thomas Jefferson is indeed the father of the child in question. Nevertheless, it is not at all "proven" that Jefferson ever fathered a child or otherwise raped any of his slaves.
By the way, I too finished grad school, but my course of study was computer science. There is no room for a minor when majoring in computer science; but if there were, my minor would have been history. I filled my electives out with history courses where I could and have read countless books on various topics in history. I've read no less than four on Jefferson himself and perhaps a dozen more on other founding fathers. I've read biographies on Lee and Lincoln and a handful on the Civil War specifically. The point I'm trying to make is I'm not some drive-by partisan on this issue. I am genuinely interested to understand what really happen in our past.