Naturally the treason argument is silly; the reason that the Confederacy was evil is not that it was treasonous.
You're of course correct, but it sure does make the pro-Confederates squirm. Remember that the people who wave Confederate flags the hardest are the people who wave American flags the hardest and are normally very offended by the idea of anyone being treasonous.
They have a sense of pride though!
Pride in what? Losing? Cause that's what they did. They lost. They would lose the war no matter what was going to happen, because England was not going to enter on their side as long as they held people in bondage and that was the only thing that could have saved the day.