I've read a bunch of articles (that I cannot look up right now) that argue that this decrease in safety is mostly perception, and I'm inclined to agree.
I grew up in the 'ghetto' of my hometown, and then from 8 tot 17 I lived in what was considered a dangerous, third-world country. Still, my parents mostly raised me as any kid in earlier times: be home before dark, don't go too far, but do whatever you want the rest of the time outside of school.
By and large, my experience has not been too different from other kids I know in safer environments, and I've had few 'scary' experiences involving other people. Most 'dangers' involved general kids-being-stupid things: crossing streets without looking, or climbing things at the risk of falling down on the pavement head-first, egging each other on to do something stupid, etc.
My point is, I can't really see the danger, and would like to know what you consider 'lacking'. Kidnapping is rare, sexual harassment is vastly more common in family circles, playgrounds have mostly become safer (and less fun, IMO), and violence of any kind by adults to children is (I think) relatively uncommon too. Even in dangerous areas.
Of course, I am no parent. And I admit I present no actual supporting evidence (right now) other than my own experience. But I'm not really trying to prove something, just interested in your take on this. Maybe I'm missing something important that I would be aware of with some context, or with the experience of being a parent