I suspect the elimination of leaded gasoline plays a role in the decline of crime as well.
For me personally, the would be criminals never being born makes more sense. If we just have less population being born from the low end of socioeconomic spectrum, there is simply less crimes being committed from this demographic.
To reject it entirely however flies in the face of a significant body of evidence: http://m.motherjones.com/environment/2016/02/lead-exposure-g...
I'd be extremely careful not to conflate the two because there's no causation explained by simply showing a graph.
Crime is a very complicated human behavior that arises from multitude of socioeconomic reasons: no money, no education, no opportunity, crime happens.
Nevin collected lead data and crime data for Australia and found a close match. Ditto for Canada. And Great Britain and Finland and France and Italy and New Zealand and West Germany. Every time, the two curves fit each other astonishingly well. When I spoke to Nevin about this, I asked him if he had ever found a country that didn't fit the theory. "No," he replied. "Not one."
The correlation even goes down to the neighborhood level:
In fact, Mielke has even studied lead concentrations at the neighborhood level in New Orleans and shared his maps with the local police. "When they overlay them with crime maps," he told me, "they realize they match up."
[0]http://www.motherjones.com/environment/2016/02/lead-exposure...