>The question thus is whether in the US it is something "imported" from the
>Third World by immigrants (as the concentration of
>this behavior in southern CA may suggest,)
It's not concentrated in southern CA. Even if it was there are a number of other conclusions to jump to or guesses to make.
>or something that is home-grown and escalating
Thefts of copper and catalytic converters have been increasing nationwide for some time.