Today's WSJ discussed an econometric debate, which is always fun (see here).
They state:

The "Freakonomics" chapter on abortion grew out of statistical studies Mr. Levitt and a co-author, Yale Law School Prof. John Donohue, conducted on the subject. The theory: Unwanted children are more likely to become troubled adolescents, prone to crime and drug use, than are wanted children. When abortion was legalized in the 1970s, a whole generation of unwanted births were averted, leading to a drop in crime nearly two decades later when this phantom generation would have come of age.

The Boston Fed's Mr. Foote says he spotted a missing formula in the programming of Mr. Levitt's original research. He argues the programming oversight made it difficult to pick up other factors that might have influenced crime rates during the 1980s and 1990s, like the crack wave that waxed and waned during that period. He also argues that in producing the research, Mr. Levitt should have counted arrests on a per-capita basis. Instead, he counted overall arrests. After he adjusted for both factors, Mr. Foote says, the abortion effect disappeared.

Levitt's response is on his website (see here) where he notes

The part of the paper that Foote and Goetz focus on is one that is incredibly demanding of the data. For those of you who are technically minded, our results survive if you include state*age interactions, year*age interactions, and state*year interactions.

3 interaction variables are necessary to get the right sign and significance? I think that is incredibly demanding. In my experience, interaction variables are kitchen sink type regressors that induce severe multicollinearity and give spurious results. It's like an economist saying his results only appear after doing 3-stage least squares. I have to think something's not really there if you can't normalize the data somehow and show in a simple graph that the pattern is there (in this case, say, by showing the change in arrest rates for abortion and non-abortion states for the relevant age cohort).

I'm partial to the opposite theory, that abortion would, if anything, increase the proportion of evil-doers: abortion is more common among forward-thinking moms who would be good moms, less common among bad moms who view life as a series of random events that happen to them.