Best Answer: Actually it is an excellent idea which would save lives. It doesn't need to be a full face helmet which is what the other responders speaking about reduced visibility and hearing are referring to. Just a bicycle or skateboard helmet would be a big lifesaver. Airbags are great but people still die of head injuries in a collision. A helmet would add some extra protection. I wouldn't mind seeing 5 point harnesses either.
The reason car drivers don't wear helmets is the same reason many don't wear seat belts; they think it can't happen to them. At least that's what the half million drivers who died in accidents last year thought.