Totally missing the point.
The United States was a colony of Great Britain. We rebelled against British rule. By Brit law, this was treason... therefore by Brit law the Founders were traitors and the US Flag was a flag of treason. How many of those who signed the Declaration were hung or shot for treason? Several, IIRC. The US had no legal basis for trying to throw off Brit rule and become its own country.
The Confederate States did much the same. They felt their interests were not being represented properly in Congress and with the Fedgov. Various political maneuvers were tried, including Nullification. Congress passed many laws that benefited the big industrial concerns and big shipping magnates of the Northeast, to the detriment of the agricultural South that needed to export and import freely to maintain its economy. The leaders of the South found themselves in what they felt was an untenable situation, dominated by a central government that was strangling their trade, and they rebelled.
They lost.
Now, don't get me wrong. I'm a Southerner, but I'm a patriot. I'm glad that America remains one nation. I'm glad slavery was ended (slavery was not the primary cause of the war, however; just one factor). The average Southern footsoldier did not own any slaves and most considered the war about State's Rights. However I think we swapped one set of evils for another: an overweeningly powerful Fedgov, whose power over the States has grown FAR beyond anything the Founders intended.
I consider the Confederate Battle Flag to be a reminder of all these things, as well as a source of pride that the South fought (for State sovereignty) for four years against an enemy that had them drastically outnumbered and outgunned.
I personally don't fly it, because I am aware that many black folks see it as a symbol of racism and I do not wish to be misunderstood, as I am not at all racist. However, the Confederate flag flies over the Confederate War Memorial on the Capitol grounds not far from the Statehouse in my state (SC).... and I consider that a perfectly appropriate place for it, as a reminder of that war, and what was won, and lost, in it.