I'm against blanket legistlation compelling helmet use. The information as to thier benefits is freely available, we can all make our own choices, and I guess parents are charged with taking the right decision for thier kids until they can do so themselves. I am pro helmets, very much so, but there's not need for the strong arm of the law as a general rule. Let those that want to wear a helmet do so, and those yet to be convinced avoid doing so. Each to their own. If that is 'informed choice'? If so I'm for it.
There are situations however when it is right and proper to insist on helmet use, which is why the main sportive rides have a mandatory helmet clause. That is the decision or the organizers, and riders remain free to exercise their right to not join in, or put on a helmet and join in. If such a ride/event/tour(whatever) prohibited the wearing of saftey helmets, i would exercise my right of choise and not join it. It is also totally fair and acceeptable for any rider to choose not to ride with another if they ride 'lidless', and vice versa.
Simples.