When I do something, I ask myself what would happen if everyone did it. When I ride my bike or walk somewhere instead of taking a motor vehicle I feel perfectly confident that everyone could do it with only beneficial results.
Realists and panic-stricken cycling opponents who screech that the bike nazis want to force them to ride will point out that everyone can't do it, so the argument is meaningless. Amazing what foaming revulsion pours out of some people when you merely suggest that they try doing something other than driving to the parking space closest to the entrance to their destination and trundling their bodies across that small distance to the doorway. True, everyone can't take advantage of healthy and enjoyable non-motorized transportation. The real prisoners of motorization must be accommodated as gently as possible into a healthier transportation mix. In a truly fair society we would each take our turn doing the motorized drudgery to try to liberate as many people as possible at least part of the time to get out and take a spin.
If everyone rode and walked we would have a system designed to accommodate that as a primary mode, not an afterthought. We would have secure parking facilities. Bikes would mutate by region so that reasonable types for each climate and terrain would dominate in their local environment. I see no down side there. Nor would the bike industry. They would have a better idea what would sell where, and how many to build.
Humans excel at creating down sides. The darker aspects of our character assure that someone will figure out how to spoil anything. But the positives of human-powered transportation far outweigh the negatives. Even in the nastiest multi-bike pileups in races, fatalities and serious injuries are rare. The worst accidents among transportation cyclists usually involve motor vehicles. Improper riding contributes greatly to the incidence of serious accidents. Education and travel-way design will help reduce problems.
Theft of bicycles and assault on cyclists already discourage some participants. Secure parking facilities address the theft problem in areas where one could ride to the facility and proceed on foot for errands in the vicinity. Assault simply grows out of the aforementioned dark aspects of human character. You might be somewhat safer sealed in your armored vehicle, but statistics on carjacking show that you might just get stuck somewhere the savages could get at you in spite of the illusion of safety created by locked doors and breakable glass. If you can't make a quick getaway, you're a sitting duck. Feel safe now?
Cars and trucks offer greater cargo and passenger capacity. Cars and trucks can cover ground more quickly on clear roads. Cars and trucks in some form are not going away. But anyone, at any time, can walk or pedal without contributing to any problems. Any number can play. It's a rare instance of infinite capacity. Why not take advantage of it?