no, no, no!
I don't know how to explain it to these people: this
The theory offered by the economist, Rick Nevin, is that lead poisoning accounts for much of the variation in violent crime in the United States.[emphasis added]
is not equal to this
Lead exposure causes crime, economist says.
Go read echidne's take on this instead. She is exactly right. (Go to her blog, then scroll down to her July 8th entry - the permalink isn't working for some reason).