Why is flying the Confederate flag allowed? It's an enemy of the United States that represents murderous cons?

The Stars and Bars is a historical flag of the USA, it is not an enemy of the USA. If you actually knew its history, which I can tell you never did your research, you would know this much. You would know what the battles were actually about, and slavery was only a minor part of the Civil War between the states. As you state, you do not even know which side flew the Stars and Bars. Personally, I would fly the flag as a reminder of the freedoms that have been removed from the states to govern themselves, the theft of the federal government to gain control of all the state's power, not unlike what is happening now in the current administration.