You know what, your car is a dangerous, lethal weapon. If you're worried about people getting killed in it, stop driving it. Otherwise you're going to have to get comfortable with some level of relative risk.
So why would you not reduce your risk as much as possible, knowing you are getting into a lethal weapon several times a day? It's just crazy logic to say cars are dangerous and kill people anyway, so no need to put a small adult or teen in a booster. That's just nuts. :
FTR, I really don't care or get worked up with what other people do with their kids. Don't put your teen in a booster, I could care less. The question was how long would *I* keep my kid in a booster, and I would do it until a seatbelt fit him properly.