I’ve read a lot of original letters from CSA soldiers to home and I don’t recall one letter where slavery was mentioned.
"A stand must be made for African slavery or it is forever lost." [William Grimball to Elizabeth Grimball, Nov. 20, 1860, Ibid.]
"This country without slave labor would be completely worthless. We can only live & exist by that species of labor; and hence I am willing to fight for the last." [William Nugent to Eleanor Nugent, Sept 7, 1863, Ibid., p. 107]
"Better, far better! endure all the horrors of civil war than to see the dusky sons of Ham leading the fair daughters of the South to the altar." [William M. Thomson to Warner A. Thomson, Feb. 2, 1861, Ibid., p. 109]
"A captain in the 8th Alabama also vowed 'to fight forever, rather than submit to freeing negroes among us. . . . [We are fighting for] rights and property bequeathed to us by our ancestors.' " [Elias Davis to Mrs. R. L. Lathan, Dec. 10, 1863 Ibid., p. 107]
"Even though he was tired of the war, wrote a Louisiana artilleryman in 1862, ' I never want to see the day when a negro is put on an equality with a white person. There is too many free n----rs. . . now to suit me, let alone having four millions.' " [George Hamill Diary, March, 1862, Ibid., p. 109]
"A private in the 38th North Carolina, a yeoman farmer, vowed to show the Yankees ' that a white man is better than a n----r.' " [Jonas Bradshaw to Nancy Bradshaw, April 29, 1862 Ibid.]
"A farmer from the Shenandoah Valley informed his fiancée that he fought to assure 'a free white man's government instead of living under a black republican government.' " [John G. Keyton to Mary Hilbert, Nov. 30, 1861, Ibid.]
"The son of another North Carolina dirt farmer said he would never stop fighting the Yankees, who were 'trying to force us to live as the colored race.' " [Samuel Walsh to Louisa Proffitt, April 11, 1864, Ibid.]
"Some of the boys asked them what they were fighting for, and they answered, 'You Yanks want us to marry our daughters to the n----rs.' " [Chauncey Cook to parents, May 10, 1864, Ibid.]
"An Arkansas captain was enraged by the idea that if the Yankees won, his 'sister, wife, and mother are to be given up to the embraces of their present dusky male servitors.' " [Thomas Key, diary entry April 10, 1864, Ibid.]
"Another Arkansas soldier, a planter, wrote his wife that Lincoln not only wanted to free the slaves but also 'declares them entitled to all the rights and privileges as American citizens. So imagine your sweet little girls in the school room with a black wooly headed negro and have to treat them as their equal.' " [William Wakefield Garner to Henrietta Garner, Jan 2, 1864, Ibid.]
"[If Atlanta and Richmond fell] we are irrevocably lost and not only will the negroes be free but . . . we will all be on a common level. . . . The negro who now waits on you will then be as free as you are & as insolent as she is ignorant.' " [Allen D. Chandler to wife, July 7, 1864, Ibid.]
I have stack of letters written home from the Pacific and European Theaters. None of them mention “fighting for our freedoms” or any of that. Mostly they are boring and asking for stuff to be sent to them.