While the reasons behind the war and its intended results can certainly be called immoral, I don’t think we can apply the same label to enlisted / conscripted soldiers. Most of those guys didn’t join up to protect slavery but rather their homes; and many didn’t have a choice about fighting at all.
Agree that slavery was a moral failing; but the cause of the war was economic — the main reason people were pro-slavery was because they owned assets that would lose ownership of or they worked in the slave trade. Yes, that reasoning is morally abhorrent, but morality often gets tossed out the window when money is involved. It wouldn’t have been a war without the money.
Protecting their homes is different from fighting for slavery in what way - I am having trouble understanding what protecting their homes means in this case. It seems like an after the war mytho to fit Shermans march to the sea burning everything as the army went or the Union army seizing Lee's homestead for what became roughly Arlington National Cemetary (and for which Lee's son was later compensated).
The problem with the "they weren't fighting for slavery" narrative is that the leaders of the Confederacy laid out their cause clearly and unambiguously very early on - the state declarations of secession, the Cornerstone Speech etc - and slavery featured very prominently in them all. It's not like those documents and speeches were hidden from the public eye, either. So anyone who volunteered knew exactly what they were fighting for.
Agree that slavery was a moral failing; but the cause of the war was economic — the main reason people were pro-slavery was because they owned assets that would lose ownership of or they worked in the slave trade. Yes, that reasoning is morally abhorrent, but morality often gets tossed out the window when money is involved. It wouldn’t have been a war without the money.