There is little question that the vast majority, if not a full unanimity, of the leadership of the Confederacy were for the institution of slavery; this is a certainty. But, my point here is that the war was not about slavery.
I've found a few quotes from Robert E. Lee that best fit the topic at hand.
"So far from engaging in a war to perpetuate slavery, I am rejoiced that Slavery is abolished. I believe it will be greatly for the interest of the South. So fully am I satisfied of this that I would have cheerfully lost all that I have lost by the war, and have suffered all that I have suffered to have this object attained." ~Robert E. Lee
It's clear that he was basically opposed to slavery, and expressed how disinterested he was in the continuation of it.
He also said what I feel to be one of the best quotes of the war:
"This war is not about slavery." No interpretation needed there!
Another of his quotes, however, needs a bit more attention:
"In this enlightened age, there are few I believe, but what will acknowledge, that slavery as an institution, is a moral & political evil in any Country. It is useless to expatiate on its disadvantages. I think it however a greater evil to the white man than to the black race, & while my feelings are strongly enlisted in behalf of the latter, my sympathies are more strong for the former. The blacks are immeasurably better off here than in Africa, morally, socially & physically. The painful discipline they are undergoing, is necessary for their instruction as a race, & I hope will prepare & lead them to better things. How long their subjugation may be necessary is known & ordered by a wise Merciful Providence." ~Robert E. Lee
It isn't natural for any person to work under another for little or no gain, so it is necessary to justify certain practices in order to go along with the crowd.
Enslavement of Africans had been a long established institution all over the Western world, so those participating in it would have seen little error in its continuation.
Robert E. Lee, being a Christian, points out that he morally objects to slavery, but legitimizes it by saying that it helps in "their instruction as a race". He apparently, though erroneously, saw their "subjugation" as a necessary evil.
Even today, supporters of segregation point to God making "white man white, and black man black" for a reason: segregation, and to break this ordained separation would be destroying His ordinances. This idea is rather silly, and is, in fact, heresy.
There are only two races identified and recognised by God: Christian and non-Christian.
"For as many of you as have been baptized into Christ have put on Christ.There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise."~Galatians 3:27-29
"Where there is neither Greek nor Jew, circumcision nor uncircumcision, Barbarian, Scythian, bond nor free: but Christ is all, and in all." ~Colossians 3:11
Had the war never started, and slavery continued to this day, I would fight to the death to end it; had the South won the war, and slavery continued to this day, I would fight it all the harder.
The institution of slavery didn't end in America because of the war, however.
And, I feel that, had the South won, it would have eventually phased-out, as it has in numerous other countries.
Slavery will forever be the blot on the banner of the Southern Confederacy's cause; it has, and always will, blind many to the true meaning of the war.