Alas, my ‘long reply’ contains the answer, and you fail to understand it.
No problem, I run into it with anyone North of the Ohio River that hasn’t studied the era.
“By the third year of the war, those troops, especially those in the Army of Northern Virginia, were not fighting for slavery, far from it. By that point, nobody was thinking much about ‘The Cause’ at all, they were fighting for their brothers - literally, and their neighbors - again literally, because of the unusual nature of the war itself.”
I understand your point that by the end of the war a few conferdate soldiers may have thought they were fighting for their brothers, But what other reason than slavery did the south cecede for?