It doesn’t get much clearer than this. Any policy decisions resulting in a reduction of mean IQ within a society are implicit choices to raise the level of criminality. If there’s wriggle room on the point, this blog isn’t seeing it.
The clearest takeaway from this research is that low intelligence is a strong and consistent correlate of criminal offending. For example, the risk of acquiring a felony conviction by age 21 is nearly four times (3.6) higher among those in the three lowest categories (1–3) of total intelligence as compared to those scoring in the top three categories (7–9). We observed differences of similar magnitude across each indicator of criminal offending and regardless of the measure of intelligence.