All I know is, there are reasons why both groups enrage the other. Good and bad found on both sides. With that said, for some humans, there is something about being behind the wheel of their car/truck that truly emboldens and empowers them. That feeling that, "the road belongs to me, anybody slower really needs to just get the "H" out of the way, especially the cyclist up ahead on the road!!!" Even some of the most unassuming humans outside of a motor vehicle, are transformed into something where rage, anger, and resentment just come easily...until they exit that protective shield known as a motor vehicle.
I think that motorists have much more to be concerned about with other motorists than with cyclists.