Picking up a few comments:
"No real difference between a push bike and a motor bike" is clearly nonsense - most motor bikes will easily exceed 70mph, a large proportion can do twice that. A cyclist is also undertaking strenuous exertion and (much of the time) needs to shed as much heat as possible.
"Is there an argument for not wearing one? Well not really," There are several good arguments, though none proven beyond reasonable doubt. Risk compensation suggests the helmeted take more risks (there's study looking at damage to bikes - bikes in accidents ridden by helmeted riders have more severe damage, on average, than those of unhelmeted riders, suggesting they were going faster or being riskier). There's also the issue that a high proportion of life-changing head injury is due to torsional brain injury, and helmets probably make that worse, not better.
There are even more arguments against compulsion - mainly relating to compulsion reduces numbers cycling, which reduces population fitness (you kill more by obesity than you save from head injuries) and makes it more dangerous for the remainder. Most places that have adopted compulsion have seen head injury numbers fall, and cyclist numbers fall by more. Cycling regularly is more likely to extend your life than shorten it, whether or not you wear a helmet.
Some points that no-one has made yet here:
Cycling is safe. The risks of being killed are about the same as when walking (cycling is slightly safer per mile, slightly more dangerous per hour). If you think it's obvious that cyclists should wear helmets, you presumably think it's obvious that pedestrians should too. Do you? Where are the campaigns for walking helmets?
What racing cyclists do on closed roads is pretty much irrelevant to 'normal' cyclists. Those that say because racing cyclists wear helmets so should ordinary cyclists don't normally advocate that all drivers wear full nomex and crash helmets, nor that you dress as a spaceman to put fuel in your car.
The fact that Bradley Wiggins thinks cyclists should be forced to wear helmets has no more influence on my views than if Ursain Bolt wanted to pontificate about the dangers of walking in Trafalgar Square. I also observe that after he won the TdF Bradley was happy for himself and his son to ride bikes unhelmeted:
http://cdn2.media.cyclin...o_0117900_1_full_600.jpgAnd finally one for H&S professionals:
How often do we turn to PPE as the first solution for a safety problem? Why is it then that the first (and normally only) way suggested for tackling the issue of cyclist safety is to demand that a particular item of PPE be made mandatory?