Just like George Washington et al? Winners get to decide who the traitors are. Historians and legal scholars are divided on whether or not the Southern States had the right to secede from the union. Lincoln was told by legal experts at the time that there was no legal basis for invading the South to "restore" the Union, but he didn't let facts get in the way of doing what I think most people agree was the right thing. However, just because saving the Union was a good thing, you can't condemn all the honorable people who thought they were fighting for a just cause. The vast majority of Confederate soldiers were pardoned as a condition of their surrender. It is a little late for you to claim they should have been hanged.
As for all this talk about the Confederate Flag - I doubt if you would even recognize the original Confederate National Flag if they paraded it in front of you. One of the many Confederate Battle Flags is the one that is buttociated with all the hate groups (see "National Flags" as well (see did incorporate the crossed bars with stars that were prominent in many of the battle flags.
Ed