For better or for worse, cycling will never be the dominant source of transportation in the U.S. Folks are too accustomed to using their cars and it still makes sense to use cars in a number of areas as mentioned before. Making people feel bad about environmental impacts doesn't really help. Showing them how it saves them money does little because once gas prices go back down as they recently have done, they don't feel bad about driving. In my experience, in your face advocacy does nothing more than divide the sides further.

All that being said, I have found an effective method for advocating (softly). People always want to ask 'why' I ride my bike to work. I always tell them that I really only do it 'because it's fun and I like it'. That often starts a conversation about how they have such and such a bike and they want to start riding again, or they thought about riding to work before, but...{insert excuse here} and that gives me a chance to dispell misconceptions and offer advice if warranted. Some people will never be convinced. We don't need to focus energy on those folks. For everyone else, I think the first step is reminding them that it's damn fun to ride a bike.