Also, one must be clear that nobody in the pro-helmet camp is under the illusion that wearing a helmet makes bike riding safe. When your head hits the ground the net change in momentum is the same whether you are wearing a helmet or not. The role of the helmet is to distribute the force over a larger area, thereby mitigating the severity of the trauma. I do not have access to appropriate statistics, but one might guess that helmets would not reduce the frequency of concussions as strongly as say, the frequency of fractured skulls. This is why an argument about "the frequency of serious head injuries" is meaningless unless the type of head injury is specified.

If you don't believe that objects are protected from trauma by padded containers, go ask someone who sells eggs whether they think it's worth the extra money to use padded packaging.