This is a fascinating discussion. Maybe something to consider is that American society is a lot more individualistic than other cultures. And that individualism is facilitated by distance - after all, proximity forces interaction: even if no on talks or communicates your brain is still processing the other presence(s), it's a cognitive load.

And the car is a consequence of that culture, not the cause. In present day and age, that tension between less and more interaction doesn't go away - it simply precipitates into cities and rural areas. The car may be unsuitable in the former, and a necessity in the latter. Tier 3 and 4 cities or communities, like the one in question, are in a constant tug of war between these opposing forces. Sure, the car itself, like any other tool, may change the society it operates within in fundamental ways, but when has that not been true for any society anywhere in place and time? And at the end of the day, has any society, of significant size, been able to eliminate a significant tool altogether from use?

Even European cities don't ban vehicles, they disincentivize their use through a combination of factors, starting with making them unnecessary. The only time a significant tool has been eliminated from use is when it has been supplanted by another - horse & buggy comes to mind.

So it goes with cars. Maybe those will be supplanted by public self-driving/flying on-demand transport in both urban and rural areas. But that won't change the tension between less and more interaction that determines how people spread out - that comes from a more fundamental property of living beings interacting with one another and the natural variation in biology/brains of people.

That brings us around to the original point - the root cause of "bloodthirst for protecting children". As many other commenters have noted - this lack of kids roaming is a recent phenomenon in the US over the past 2-3 decades, while cars have been around for 10 or so, and in widespread use for 7 or more. And the pendulum appears to be swinging in the other direction with many legislatures taking up the right to let kids roam.

Looking at the combination of those 2 factors - cars' lengthy history at the interplay of human interaction, and kids not roaming' being a transitory phenomenon, I'm having a really hard time drawing a connection between the "latent fear of strangers" coming from "car-dependent living". In fact, I would argue that the fear of losing a child in an urban setting with more strangers around would be far stronger than a stranger driving in from outside and making off with a child.

And police brutality has also been around much longer than has the lack of kids roaming. In fact, kids roaming is just another in a long litany of excuses for projection of power from police or any kind of uniformed service.

This makes me think that the connections between "bloodthirst for protecting children" and "latent fear of strangers" coming from "car-dependent living" might be a bit tenous. I would like to see more actual evidence for that before accepting it at face value.

I could even argue that the bloodthirst for protecting children is likely more related to the declining birth rate - fewer children means each individual one is valued more in nuclear families - split attention is a real phenomenon. Another factor could be greater awareness and depiction in popular US media of crime and the horrors that taken children undergo.