There's a theory that abortion reduces crime by reducing the percentage of unwanted kids in the population. To make this argument, they have four pieces of evidence. The first is that five states legalized abortion two years before Roe and all five had earlier crime drops. States with higher abortion rates at that time also had bigger crime drops. Third piece of evidence is people born after Roe v Wade have lower crime rates. And number four is data from other countries confirms the result.