The idea that not enough cyclists wear helmets is an example of the logical fallacy called “begging the question“. It relies on a number of assumptions:
- That helmets are necessarily a good thing
- That cycling is dangerous
- That helmets make cycling less dangerous
- That cyclists who decide not to wear a helmet are being wilful or capricious, rather than making a rational assessment of risk and benefit
None of these assumptions is proven, particularly the last. It is my firm belief having extensively studied the subject that a cyclist may make an entirely rational and defensible decision not to wear a helmet, either habitually or for a given journey.
In the end, cycling is not actually particularly dangerous. The same logic which says that “not enough” cyclists wear helmets could be used to justify the statement that “not enough” drivers or pedestrians wear helmets. Who decides what is “enough”? The helmet promoters? I’m afraid they lie rather too often for me to take their word for it.
Cycling is not especially dangerous, and helmets do not appear to change that one way or the other.