How come there is a lower crime rate in Western Europe, where there is Socialized medicine?

Who knows?

Lower levels of lead in the air due to historically less use of cars, cars with better fuel mileage, diesel cars, etc.?

http://www.motherjones.com/environment/2013/01/lea...

Greater social mobility and lower income inequality make crime less attractive?

http://www.economicmobility.org/assets/pdfs/EMP_In...

http://www.brookings.edu/articles/2011/1109_econom...

Particularly among minority populations.

Or maybe it is just the culture? As Bevins noted, "It must be remembered that America was settled by people whose response to social problems was to run away."