When you slaughter problem children, you tend to have less problems.
Since abortion targets poor minorities, one should hope that the death of their progeny would cause less problems for the society that gave them the tools to kill more of their own kind.
The better question I would have for you is to roll back the crime clock in the US to when abortion was illegal, and lower than it is now. You didn't provide a fully accurate depiction of US violent crime rates, as they took a HUGE jump in the 1960's. Prior to that, crime was much lower.
Back from the dead, I'm afraid.