...3. Just as we cannot impose 21st century values back into the 19th century...
Of your long list, this is the only statement I would contest. This is a common "truism" -- something which sounds eminently correct but is not.
imho if we accept the truism "that we can't impose 21st century values back into the 19th century" it is to allow both Confederate and Unionist apology, in other words it allows an obfuscation of history.
So after all, we certainly can, and should, impose our values when we are called to do so, as inherently moral human beings. The truism fails because it hinges on the adjectives "21st century" and "19th century," by which we are expected to suppose that inherent morality has changed over that time, that our quaint Antebellum/CW ancestors were locked into their quaint moral universe.
It's bunk. Our Antebellum/CW ancestors were every bit as morally sophisticated as we are today. They understood right and wrong in the very same way we inherently do today.
They acted or failed to act on their inherent morality the same way that we do today. They were not a less advanced form of human than we -- this is not a case of evolution of the species. All this is abundantly clear in the published writings of the great moralists of that period and in some of the extensively perceptive correspondence of the common folk of that period that we cite so often here in this forum.
Also imho, to accept the truism is a disrespect to our ancestors. It supposes that back then they, like children, "couldn't help" but to accede to some prevailing moral center.