It's not about blame, it's about preventable injury. It's about reducing the chance you'll get a call from the hospital saying "your kid has had a bike accident and she is in a coma." I've had friends who work in ERs have to make those calls. In many cases if the kid had been wearing a helmet they would have had a mild concussion. Instead their life as they knew it is over.

If you don't want to wear a helmet, that is of course your decision. I just object--strongly--to your contention that helmets aren't necessary in commuting. That statement is just not based on any measurable facts.