100%, and cars are a reasonable worry that we should do something about. There are well known traffic calming measures that we know slow down traffic substantially (speed being one of the greatest causes of pedestrian fatalities) and even in my very walkable city we're largely not using them.
support traffic calming measures (like narrowing car lanes, adding streetside trees, converting parking to bike lanes, etc.), not for specious reasons like this, but because they reduce distracted driving, and thereby reduce collisions and injury/death. it's at best misdirection to talk about reducing speed, and at worst, leads to poor policy that not only doesn't address the problem (reducing injury/death) but creates unintended consequences (like traffic and more distracted driving).
Of course they both contribute to the problem. So why not both? Traffic calming is the answer, either way.
Like dogs?!
Well intentioned and mostly just amusing. At least no-one called the authorities when they realized we weren't planning to confine our kids to the yard or accompany them on every idle play-outing all damn Summer.
Varies by neighborhood, though. Our current one's busy-body and kids-only-play-with-parental-escort enough that we had a couple neighbors stop by to warn us that they'd seen our kids several streets over, thinking they'd gotten away from us. Not quite busy-body enough that anyone called the cops (I suspect we were right on the edge of that happening, and maybe just got lucky). Our last neighborhood had wonderful mixed-age "gangs" of kids wandering around playing all the time, and it would have been entirely safe there. That was a much younger neighborhood (in terms of both the ages of the houses and the average age of residents) than this one (not sure whether that's related), and, I suspect, there were some class issues at play (the other had a very high-prole character to it, in Fussellian terms, while this one's 100%, gratingly, middle-class as hell)
As for chances of assault, your main worry by a country mile should be cars, not predators. All forms of attacks on kids by strangers are incredibly rare. Leaving your kid in the company of a specific adult or set of adults is far riskier than letting them walk to the park (yet people do that all the time). Shit, statistically siblings or cousins are far "scarier" and worthy of concern, in that regard, than the risk of regular walks to a park 2 blocks away.