Why were rednecks so racist back in the day?

I was watching this film called a time to kill or something like that, it was based in like the 50's or 60's where 2 racist rednecks violently raped a 10 year old black girl, pissed all over her, put a noose around her neck trying to hang her and chucked her off a bridge. Apparently it was a true story.