I'm agains helmets being obligatory. Many people regard cycling to be a dangerous activity. Having grown up and living in a cycling town, with a good cycling infrastructure where practically no one wears a helmet. Depending on the type of riding, one should be allowed to choose for themselves. Yes, when you fall on your head it's better to have a helmet, but it's about probability (risk), otherwise, wearing helmets when walking (especially in the winter, when there's ice) could also be obligatory by law.