When leve and i wrote about that argument in economics, we were very careful to make clear that this was not an argument about the upsides or downsides of abortion per se. We tried to write it as an argument about how it can be that policy leads to behaviors that lead to downstream, unintended consequences. One factor that did cause a droping crime was a big increase in impris ment. The really interesting question is why did crack mostly go away? It's hard to argue this but one good answer seems to be that crack is such a terrible drug.