From a societal standpoint, there is also the possibility that if everyone rode bikes, one would get a better mix of poor and rich for part of the day. When one has a chance to see and interact with others, fear from ignorance goes down on both ends. We don't have a real mix in our small town but I meet people almost every time I bike but I never meet anyone while I am driving. So it provides a better sense of community than driving does.
You could ague that the U.S. consumes a huge amount of the world's resources compared to its population which leaves poorer countries fighting amongst themselves for what is left. Global climate change will also be affecting poorer countries much more severely than it will rich countries.
But I bike because it is fun and I don't have to schedule 'exercise time' into my day, it just happens while I am doing errands. I am more in touch with my community and natural surroundings and it helps my mental health also.
Few people will be swayed by an intellectual argument so use emotional appeals but base them on facts. I don't know if anyone has done a study but I bet neighborhoods where people bike and walk more have lower crime because most people will know their neighbors, like an unofficial blockwatch program (this would be a statistical difference not a 100% thing). So I would push the emotional arguments of safety, community connectedness and fun. What if your commute to work and home each day was similar to what many people do on weekends, ride in the park. With few cars, our streets would be parklike and be a pleasure to use. Automobiles also don't pay anywhere near their fair share for the use of the public space that is our roads.