> But lead by itself can't be the major factor behind the crime drop. Countries such as Brazil have banned leaded gas even before the United States, and crime rates are still rising dramatically.

This is not logically sound. Brazil could have other factors which increase crime more than getting rid of lead reduces it. The fact that Brazil's crime has increased does not, in any way, tell us that the lead ban couldn't possibly be a major factor in the US's drop in crime.