While you are correct that at the big-picture/political/money level, slavery was the issue...where Southerners get confused is at the individual soldier level. Lee for example, was against slavery, and freed all of his slaves before the war began...(contra Grant), however he strongly believed in states’ rights, so too, the majority of the soldiers who fought for the South were too poor to own slaves—hence they each had their own personal motivations for fighting, some noble, some not.
I find that the whole North/South debate on whether slavery or other issues were the cause of the conflict boils down to big-picture/political/money issues (of which slavery was it for the South...) verses individuals’ personal motivations for fighting (often simply “because the Yankees are coming...”) which really is an apples to oranges comparison.
Another complication is why did the NORTH go to war? It wasn’t to free slaves, as Lincoln had repeatedly said he would keep them enslaved IF IT WOULD PRESERVE THE UNION. So Northern motives at the big-picture/political/money were not all about freedom and idealism (as their descendants like to think) but rather were primarily just to preserve the union...for all kinds big-picture/political/money reasons.
As to individual Northern soldiers motivations? Of course some were fighting for freedom...some weren’t, there were all kinds of reasons for being there. But at the big-picture/political/money level, Lincoln and the North only pushed emancipation mid-war, when they saw they were losing...and they knew this new moral crusade would rejuvenate motivations.
As a Southerner, what convinced me that at the big-picture/political/money the reason the South separated was due to slavery, is the record of the various state-legislatures debates on secession. In every one, the debate centered around preserving slavery—which of course was a keystone in their economy at the time....so if you follow the money trail the truth comes out. Of course state legislatures’ votes, and individual soldiers’ motivations are two different things.
So too, follow the money trail in the North...and loss of union was bad news for Northern money...hence preserving the union was the highest priority, NOT freeing slaves. Noble motivations for abolition amidst certain soldiers...sure, but, so what?
Lee had mixed views on slavery, regarding that Peculiar Institution as a necessary evil and "the white mans burden". He did manumit his slaves but evidence suggests that it was more a matter of practical necessity rather than ideological bent.
U.S. Grant owned no slaves. Well that's not entirely true. He did purchase one slave from his FIL so that he could manumit him.
"As to individual Northern soldiers motivations? Of course some were fighting for freedom...some weren’t, there were all kinds of reasons for being there"Wasn't there a draft in effect part way through the war?
Lincoln issued the first Emancipation Proclamation on September 22, 1862, 18 months after the war started. The US had just defeated Lee's attempted invasion at Antietam and the blockade was in full swing. In the west, New Orleans had fallen, Grant had already occupied Memphis, had troops in Mississippi and was about to begin the Vicksburg campaign. Now, in what sense were they losing?
If the North was not trying to end slavery why would the south need to secede to preserve it?