I don't really think that wearing a helmet should be "a matter of choice". Consider the road hazards: pothole, squirrel, pedestrian, wet leaves, wet manhole cover, other cyclists, railroad tracks, etc. All of these could cause a cyclist to hit the pavement, but would not be much of a problem for the driver of a motor vehicle whose only real risk comes from other drivers.

Nonetheless, driving around the city at 25-30mph, drivers of cars consistently wear seat belts (and could be fined for not wearing one), yet cyclists traveling at 15-25mph consistently choose not to wear a helmet. Drivers wear seatbelts not because it looks cool or is the most comfortable, but because of a massive public safety campaign in which people were educated about the risks of not wearing one, and in the aftermath, car companies were required to install more and more safety devises (air bags, anti lock breaks, etc).

We need the same kind of public safety campaign for cyclists such that nobody would even think to get on their bikes without fastening their helmet, just like they don't think to drive their car without fastening their seat belt.