Because that would allow the issue to be settled. I thought of that possible solution immediately, but you know it would never be acceptable to those who want to keep things stirred up. The suggestion would immediately be greeted with comments not unlike those we've read here on CF--The Confederacy was evil, so any such flag is unacceptable, they lost so their memory deserves to be erased, etc.
You know that's what would be said, even though we started out with the claim that the battle flag was the one that was seen by unnamed Americans to be a symbol of hate because the KKK used it and the Charleston shooter was pictured holding it.