Even in the 70s, with all the weirdly hands-off parenting styles that were going on, sitting in the front seat for me and my brother was a BIG deal. It wasn't something that started young, and my mom didn't always let one of us sit up there.
It's all about fitting in the seatbelt, and being big enough that the seatbelt hits where it's supposed to hit and doesn't do MORE damage. Before cars had seats that went up and down (or before we could *afford* the cars that did that), and before cars had seatbelt guides that went up and down, seatbelts in some cars were dangerous even for me at 5'3", and really bad for my mom who only hit 5'1". I remember putting the cross-body belt behind me, because I was scared that it would cut my throat in an accident, because that's where it hit, on my neck.
DS is 8 and therefore he has reached the
age that he can ride without a booster in WA. He didn't fit the seatbelt yet, though, until last week or so. In another car, if he doesn't fit, he'll use the lowback booster.
I just looked up the front seat info, and in WA: "Children under thirteen years old must be transported in rear seats where it is practical to do so." So there we go. We have a car where it's not necessary for him to sit in the front, so he'll be in the back until he's 13. By that time he'll probably be well on his way to 6', so he'll fit up front better than I do!
My brother and I used to secretly undo our seatbelts in the bucket seats of my mom's Pinto station wagon. We thought we were so clever and sneaky. We were LUCKY that we never got into an accident while doing that. If we had gotten into an accident, we would have met the windshield.
Anyone who lets their kids unbuckle while driving is taking that risk, that something will happen during a very vulnerable time, and they need to THINK about that risk. We cannot control everything that happens while we are driving. A car could t-bone us, a deer could jump out, a dog could cross the road in front of us. We could hit ice, we could have a stroke (something very much on my family's mind, as my MIL has started having them...she's had 6 since Labor Day Sunday and she was lucky she was at temple instead of in her car driving home when she had that first one...she hasn't driven since then as far as we know), ANYTHING could happen that's not under our control. Having a person unbuckled for 2 seconds could result in utter tragedy, if something happened right then.