In any case, even if you can still find some occasional examples of people allowing unsupervised play in some situations, it's definitely unacceptable to simply send the kids out and tell them to be back for dinner, the way it was normally done some decades ago.

One of my professors lives in a cul-de-sac where literally every house has ~2 kids of roughly the same age, and so most of the parents allow their children to just go outside and play with the gang until dinnertime. I believe at least one of the parents is typically watching, which is also a departure from the old days.

Hearing him describe it to the grad students / other professors, though, it was clearly a "this is an abnormal neighborhood which is like where I grew up, which is fantastic," and he's the only person I know of with a neighborhood like that (though certainly similar neighborhoods must exist).

Twenty years ago was still a very different time in this regard. (Anecdotally, I notice that people who are in their mid-twenties and older have childhood memories very different from what is considered acceptable nowadays, both informally and legally.)

But why? I thought crime rates in America had actually declined significantly since 20-25 years ago. If so, then why would it be more unacceptable today to let children play free than it was twenty years ago; has irrational helicopter parenting grown for other reasons, e.g. status competitions, with no correlation to actual danger levels? (Or is there something subtle I am missing, for example has violence declined in ghettos/low-class areas but the middle and upper areas we are talking about are less safe?)

That's... seriously counterintuitive to me. I'm certainly not deeply embedded in parenting culture, and my childhood memories date to the early 1990s as well as being unusual in some ways, but I'm skeptical of drawing strong conclusions from an advocacy site. What else are you basing this on?

I would just ask my relatives about parenting standards, but unfortunately they're divided between having very young and adult children. And that's a pretty small and biased sample anyway.