“The Confederate constitution explicitly established slavery. Does that mean the Confederate government was explicitly unjust because it lacked the consent of the slaves?”
Is your use of the word “explicitly” gratuitous, or are you deliberately contouring the discussion in a way that avoids the uncomfortable fact that the United States constitution included pro-slavery provisions?
"No bill of attainder, ex post facto law, or law denying or impairing the right of property in negro slaves shall be passed."