That was certainly more and more true as the war proceeded, but keep in mind that prior to the war per capita income of free people was almost twice as high in the slave states as in the North, with the South having 30% of the nation's free people but 60% of the wealthiest Americans. What the Confederates discovered, however, was that it was difficult to convert cotton into food when trade with the Northern states was cut off.
Also, as in most films, they take create license to protray something that encapsulates. I think that was the reason for the dialogue between Jackson, the cook and God.
I think the filmmaker was trying to pander to the Confederate sympathizers, which I dare say are more heavily represented in TNT's demographics.
It also was the reason for the dialouge between the house slave and the Union general. I think it brought out the complexities of slavery without making it the focus of the movie.
You can't make a credible Civil War movie without focusing somewhat on slavery. The regimental history of my great great grandfather's Illinois cavalry regiment has numerous accounts of freed slaves providing valuable intelligence to Union soldiers and singing and jumping for joy as they abandon their Virginia plantations in droves and head north to enjoy their freedom. Is it expecting too much of a fair filmmaker to have included at least one such person in a four hour movie? Is it asking too much of a fair filmmaker to include a mention of the fact that Lee's men made slaves of any able bodied negroes they found when they invaded Pennsylvania (including during the aftermath of Antietam in 1862)?
Judging from all the books written about the Civil War, it has been covered from every angle and from every point of view. I thought it was a good movie and as expected will be enjoyed again through dissection and a by-product of that is more insight and reflection.