I assume that they purpose of the scenes on the bridge are to make sure that future generations keep up their hatred toward whites. Yes, whites in that era were pretty darn bad to treat blacks like they did, but that was another era and they are not treated this way anymore. It keeps their racism business going and spreads hate.
Reminds me of the movie "A Time to Kill", based on a Grisham novel, in which two white dudes run roughshod over a predominantly black town. They push around all the pliant Stepin-Fetchit blacks and end up raping a little black girl. I guess the town was in some sort of 1930's time warp.
You never hear about how many whites were walking with the blacks for civil rights including Charleston Heston. That would make it sound like only blacks went south to help change the laws in the south. They cannot even tell the truth about Selma and how many whites were murdered in the south helping out.....