One of the problems of interacting with people on the roads is that we rarely see each other as individuals. We see a car, or a van, or a bike, and we don't see the person inside. And when we don't see the person, we don't feel the need to act towards them in a human way. How else to account for all the stupid, reckless and plain rude behaviour that you see on the roads every day? When we are walking along a crowded street, we make eye contact, we manoeuvre around each other, and we smile. On the road, the face isn't visible, and that gives us permission to treat others as simply obstacles in our way.
Bikers often make this worse for themselves. Even a clear visor cuts off most of the face from the outside observer. Black visors blank it out completely. Add to this a bit of creative positioning and making good progress (!) and it's not surprising that other motorists often view us as hooligans and hazards. Road safety material usually either nannies bikers by telling them to wrap up warm in a nice bit of fluoro-yellow, or accuses car drivers of being blind and stupid. Here's a bike safety video that does neither, and I think it's rather good.