Having been an EMT, I've seen that most times the family is not "lucky" enough for the unrestrained children to die cleanly [I'm saying that to make a point - I've seen despair as you can not imagine and shared in it, knowing there could have been a simple car seat solution to avoid that!] In fact, they (or adults in the same situation) become severely disabled, barely alive, and now the end effect is not a burden the family alone endures - we all do. We all pay for catastrophic medical care in the insurance system. I'd rather my insurance premiums would stay manageable - something that won't happen since I always help pay for those who allow their kids or themselves to require expensive intensive care when they could have prevented it.
And, those who talk about not wearing a seat belt when they were young - neither did I. But - I also lost a lot of loved ones to car accident deaths that would have been preventable.