> And cars used to be safe even without seatbelts!
No, they weren't, which is why this is a poor analogy. We discovered that seatbelts could save an enormous number of lives with minimal impact on individuals, so we mandated them.
With child safety it's difficult to get comparable numbers (overall crime spiked in the 90s, so it's difficult to say whether kids were less safe because they had less tracking or just that overall crime was higher then), a big reason experts give for the reduction in crime affecting kids is they're simply inside a whole lot more.
They'd be even safer if we just put them in a plastic bubble I guess.