The safety and freedom that Krugman describe are rare now even for the wealthiest Americans – by age 9, I would typically leave the house on a Saturday morning on my bike, tell my parents I was “going out to play,” and not return until dinner; at age 10, would go down to the ocean to swim with friends without supervision all day; and at age 11 would play flashlight tag across dozens of yards for hours after dark.
Here's the thing: leaving aside demographic changes in Krugman's native Merrick, NY, most American suburbs today are very safe places. The murder rate nationally in 2009 was 5.4 per 100,000 people, vs. 5.1 in 1960. Violent crime rates nationally were at lower in 2009 than at any point since 1973. It's true that the 2009 violent crime rate remained two and a half times that of 1960, but most of that crime was concentrated in poor inner city neighborhoods (and increased reporting of rape probably accounts for some of the difference over time). I doubt that most little Manzis or Krugmans living on suburban streets today are at significantly more risk of being crime victims than their grandparents were in 1960.
What's changed is parents' perception of risk -- and tolerance for it. Perhaps the crime-ridden 1980s changed the culture, or perhaps increased affluence (we'll get to that...) inevitably makes parents more risk averse, or perhaps we're just all made permanently jittery by too much information, or maybe our dual-action superparenting ethic renders us incapable of leaving them kids alone. As Megan McArdle points out, too, back then, neighborhoods full of stay-at-home moms increased the sense of on-the block safety. In any case, as parents we've gone collectively insane. As Lenore Skenazy has documented, parents in many suburbs won't let their kids walk two blocks to school: