I have to disagree with you here, although when I toured in the south, stuff was hurled at me by those who appeared to be on the lower end of the economic scale.
Around southern California the typical person who throws things, insults, or displays road rage toward cyclists seems to be middle class (or above) white punks, sometimes in $50k trucks, sometimes any other car. A lady friend of mine was hit with a Slurpee by 2 idiots in a BMW who then ducked into their private school where another friend saw them go and had them arrested. I figure Mommy took the Bimmer away for a couple days.
It was a doctor who was busted out here for brake-checking two cyclists with his Benz, he got some jail time for it, too.
Sick, sadistic bastards come from all socio economic backgrounds.