I am arguing that the seatbelt does too little to keep the driver in control of the car no matter the situation to the point where it makes no difference. Passengers are another story simply because they cannot anticipate changes in the attitude/speed of the vehicle.
I've had the seatbelt lock up on me under heavy braking but it was never to the point where I felt that if it wasn't there I wouldn't have been able to keep myself upright, I might have leaned forward an extra inch but most cars just don't decelerate quickly enough under braking to make a difference. Obviously I'm not talking about something crazy like a Veyron going from 242 to 0 in 10 seconds I'm talking about cars that most people would drive. In my experience suspension and seats makes much more of a difference in how well you stay in your place when driving.
If you're bracing your decelerating weight on the wheel, and my seatbelt is holding part of my decelerating weight, I'm in a better position to actually move the steering wheel (and operate the shifter). The Veyron comment doesn't hold any water either:
Veyron:
252 - 0 mph in 10 seconds = -11.265 m/second^2
1g = 9.8 m/second^2
thus average deceleration is 1.149g (which is biased, because from 60-0 has almost no air drag advantage compared to the 252-0, thus in a 60-0 stop the deceleration rate would be lower)
Still, if we keep this value, in conjunction with published Veryon braking figures of: 60-0 = 104ft
the vaunted Veyron takes ~2.39 seconds to pull up from 60 at -1.149g
Audi A4:
60-0 = 107ft
Yes, the Veyron has incredible fade-free brakes, but they don't result in shorter stopping distances from normal speeds on the first try than plenty of average machinery. Even if we assume differences in testing venues skewed wildly in favor of the Audi (unlikely), there might be
at most a 5-10% difference in the decelerative forces possible from 60-0 that a Veyron can produce compared to your car. Most modern cars have incredible brakes, and most people don't realize it.
I can't believe the government lets me ride a motorcycle. It doesn't get much less safe than that (even in full leathers + helmet + back protector)