You're right, nobody is alive from 150 years ago. Then explain the proliferation of Confederate flags? Those guys lost the war, but still seem intent on keeping the flames alive.
Racism dies hard, it gets passed from generation to generation. And don't forget, desegregation didn't happen until the 60's, and there are lots alive from then. Blacks were forced to the back of the bus, had separate drinking fountains. They fought separately during WWII and even had to fight racism in the Air Force. Those people are still alive.
In other words, history.