Rather than ponder why cyclists are viewed poorly by drivers, I think it is more productive to speculate on how we can improve the image of cycling in general.
If Americans love one thing, it is an athlete. Thus, I think we need to make a greater effort to promote cycling as an ATHLETIC ACTIVITY. Joggers and long distance runners use road shoulders in many cases, just as cyclists do (sidewalks are Ok but not ideal, as they can be bumpy). As a runner i recall no instances of hostility from autos (though, to be fair, i have very few examples of hostility when on my bike either).
I would 'market' cycling as
(1) low impact/aerobic activity.
(2) more enjoyable than indoor gym workouts or dull training machine routines.
(4) racers/clubs should emphasize the athletic aspect/olympic aspect of the sport, and
(5) touring folks should emphasize its low cost, low environmental impact, and closeness to nature and native culture in foreign countries.