[Aka]

I think the kinetic energy in the bag is less than your face hitting the steering wheel. The airbag doesn't weigh much, yes it's moving fast, but the force it would exert on you isn't that bad, considering the force of suddenly decelerating in a crash.

If you cross your arms infront of your face while driving*, you weren't going to avoid the crash anyway, and airbag or not, you're probably breaking your arm(s)/wrist(s) into the steering wheel.

*while still holding onto the wheel