From what I've heard of it they're not even talking about teenagers most of the time. They're talking about - like - nine-year-olds or younger. In any case, I don't think much of it because most of the time when people start to adhere to some "latest line of parenting", it's because they, the adults, themselves, have the either/or thinking that people are supposed to grow past once they become parents.
People need to use common sense and be willing/able to face the reality that a young kid out walking alone isn't the wisest thing (in most instances). True, there's a good chance the child (and zillions like him) will be OK, but the "nothing-bad-will-happen" thinking that some people are too insecure or stupid to out-grown (when protecting a child is required) means that all won't be OK for all children - and it's too late when some sick freak singles out YOUR child.
This is not the 1950's, and most of America isn't much like 1950's/1960's television anyway.
It's not convenient to aim to give a child freedom and independence, and it takes some thinking things out. It's less convenient to try to do the same for, say, a few children. One almost has to take things situation-by-situation and then factor in any differences from daily situation to daily situation, and then factor in, too, the individual child and age of each child. (Like, is a five-year-old walking on a quiet, suburban, street to the house across the street as his mother watches until he gets to his friend's house (where the mother there can be trusted to watch the children; or is a ten-year-old walking on either a wooded area of road or else around a downtown area where there's lots of opportunity for him to encounter bad stuff (including traffic, by the way).
In any case, it's not a matter of either/or - either someone suffocates a child and tries to stop him from all children's natural tendency to want independence (at the right time) OR someone just doesn't watch/protect the child and hopes for the best. It's not even just concerns about sicko freaks. It's all kinds of things. And it's not even just about walking alone. A couple of kids together can think up some pretty dangerous stuff to do.
Parents need to a) be grown-ups, b) think like grown-ups, c) protect their children, d) have some common sense, and e) figure out (sometimes creatively) how to let children grow and gain increasing age-/development- appropriate independence.