I don't have data, either. But I do recall the debates about making seatbelts the law. The talk was always about whether one was safer being thrown from a car than staying in the car. I never heard mention about being thrown from a car causing another accident.

After the law passed, I heard many people say they wouldn't wear the belt out of fear of being trapped in a burning car.

It's just that these discussions have been completely forgotten since, and the assumption is that seatbelts are always better.

I wear a seatbelt because the odds are better. I'm aware there are cases where it isn't.