Exactly what this world needs: more government regulation. But why stop with bicyclists? God knows someone needs to reign in those hooning skate boarders, roller bladers, tricyclists and pogo stickers, too.
The issue of helmets is less straightforward than one might think, owing to the law of unintended consequences. There have been studies concluding that helmet laws discourage adult bicycle riding to the extent that the net effect on public health is greater from the loss of fitness that could be had from cycling than from the reduction of rate of injury mandatory helmets provide (bit.ly/1WQiYDS). Also, a 2007 study (bit.ly/1Y37wY6) indicated that motorists leave a bit less clearance (~8.4cm on average) when overtaking a helmeted bicycle rider as opposed to a bare-headed one, consequently exposing them to a slightly greater danger.
Further, helmet testing standards only certify protection from a fall of 2.2 metres height, far less force than one might receive from a
Fabio Casartelli-style crash, and 250 grams of expanded polystyrene wrapped around one's brain case will do precious little to prevent a 2000 kilo automobile squashing it like a grape.
I am not arguing that helmets do not reduce injuries but there are counter-intuitive realities that make mandatory helmet use for "casual" cyclists of questionable value.