If Those Kids Could Read They'd Be Very Upset - if those southerners could read they'd be very upset

Basically a somewhat lengthier version of this.

Confederate apologist: "The Civil War was about states rights!"
Other person: "States rights to do what?"
Confederate apologist: "…own slaves…"

Usually when confronted with this those 'Lost Cause' folks will burble something about liberal historians warping the truth or something to that effect. Insist that this is a direct primary source authored by the Confederates themselves and they'll try to change the subject. It's like you can see the cognitive dissonance at work.