kevin, the issue is relative risk .

helmet use is often predicated on the assumption that relative risk of head injury to be higher on a bike, than off the bike, yet this hasn't been shown.

in terms of raw numbers, head injuries occurring in bathrooms are far more numerous than the same associated with bicycle use but as you argue, there are factors involved that make head injuries in bathroom look like a greater risk than head injuries on a bike when they may not be. The trouble is, you haven't presented a reasonable breakdown to show that is the case.

This is a central argument in helmet use; lack of proper context. Figures of injuries and death are presented by helmeteers that do not show the relative risk of head injury for a cyclist. There's no idea how likely such injuries are to occur, just figures to show they do. Well, they happen to people in bathrooms too, is the risk of head injury to someone on a bike any greater, than the same to someone in a bathroom? Can you show a proportionately greater risk for head injuries to people on a bicycle, than off a bicycle (or off a bicycle and in a bathroom)? You haven't shown this yet.

I think we can both agree that risk involves many factors, and that a solution that involves changing just a single factor, wouldn't be as effective as a solution involving changing numerous factors, so why get all worked up about changing just one factor?