For the record, I do think the Southern States were fighting specifically to preserve the economic institution of slavery. Although, the average white southerner who fought and died on front lines did not own slaves (it was a 1%-er thing)... so it was a bit more complicated than that. Part of it was "patriotism" for the state, and so forth.
All I'm saying is that the North, in general, wasn't fighting the Civil War out of some sort of moral abolitionist high ground. It was basically the culmination of a trade war. The moral objection to slavery came as an after-the-fact justification... just as in many wars all around the world there's the "justification" which often is different than the "reason."
Basically, it was a complicated, messy, war. I don't think there was any real moral high ground to be had, other than probably in the average soldier simply doing his duty. But again that's true everywhere, even today.