A point you don't make here concerns Southern officers other than Cleburne. For example, in his memoir, William C. Oates of the 15th Alabama Regiment includes a chapter about "arming the negroes". He expressed frustration on this issue, having gone to Richmond in April 1863 to speak with his congressman about it. I never see anything from Oates cited among all the standard "Black Confederate" media.

You are drawing in an unreasonable inference from this point: because the Confederate government failed to enact a plan of emancipation and arm slaves, the war itself must have been to preserve slavery. This is not logical. The Continental Congress failed to do anything along these lines, either. Oates emphatically states that had the Confederate armies been told they were fighting strictly to preserve the property rights of slaveholders, they would have disbanded within a matter of weeks.

Col. Oates has some interesting things to say about why non-slaveholders fought so long and earnestly against Mr. Lincoln's army, but I doubt anyone cares. The experiences and opinions of this former Confederate line officer doesn't fit into anyone's preconceived opinions about American history.