I am quite sure until a few days ago 99% of the residents in Madison did not know about the marker!
You’re probably right. I do genealogical research and have visited lots of cemeteries. Even when I go to where more recent relatives, such as my wife’s parents, are buried, I wander around to see if I can find anything historical. I would notice something like Confederate graves right away. Most people wouldn’t have the interest in the first place and would just go on by. The ones in Madison are probably aghast to find out about this because, if they had known about it before, they could have been outraged in a more timely manner.