So, for those (sarcastically) saying that we should start wearing helmets in the car or the shower...
Seatbelts immobilize you to make you a "piece" of the car. When you're wearing a seatbelt you're no longer a piece of luggage being thrown around inside the cabin. This immobilization means that you're not going to be ejected from your seat, and if your seat is properly adjusted (head rest height, distance from the steering column/airbag, etc) it will pretty well protect your neck and head from injury.
According to the NHTSA,
approximately 75% (that's 3 out of 4) people who are totally ejected from the vehicle in a crash are killed.
In a motorcycle crash, you have a 100% chance of being "ejected" from the vehicle, and are
35 times more likely to die than a person in a passenger car crash. Wearing a helmet means you have a
37% higher chance of surviving the motorcycle accident.
Regardless of what people say about their "riding skillz", not every accident is avoidable. By getting on a motorcycle, you are taking on additional risk that is simply not present when "stepping into the shower" or "walking down the sidewalk", or even riding in your car with your seatbelt off. Of course, not every crash will kill you. But not wearing a helmet means that you have a statistically higher chance of being killed in a motorcycle crash. Period. And you can't fight statistics.