basically, race has nothing much to do with abortion/lower crime rate:
....2)Race is not an important part of the abortion-crime argument that John Donohue and I have made in academic papers and that Dubner and I discuss in Freakonomics. It is true that, on average, crime involvement in the U.S. is higher among blacks than whites. Importantly, however, once you control for income, the likelihood of growing up in a female-headed household, having a teenage mother, and how urban the environment is, the importance of race disappears for all crimes except homicide. (The homicide gap is partly explained by crack markets). In other words, for most crimes a white person and a black person who grow up next door to each other with similar incomes and the same family structure would be predicted to have the same crime involvement. Empirically, what matters is the fact that abortions are disproportionately used on unwanted pregnancies, and disproportionately by teenage women and single women.
3) Some people might think that my comments in (2) above are just ducking the race issue because it is politically correct to do so. Anyone who has read Freakonomics knows that I am not afraid to take issues of race head on. Much of the book deals with challenging issues of race (e.g. black-white test score gaps, black naming patterns, etc.). I mean it when I say that, from a purely fact-based and statistical perspective, race is not in any way central to our arguments about abortion and crime.
4) When a woman gets an abortion, for the most part it is not changing the total number of children she has; rather, it is shifting the timing so those births come later in life. This is an important fact to remember. One in four pregnancies ends in abortion and this has been true for 30 years in the U.S. But the impact of abortion on the overall birth rate has been quite small.
5) In light of point (4) above, it is hard to even know what Bennett means when he says "you could abort every black baby in this country, and your crime rate would go down." Implicit in his comment is the idea that some external force, like a government, is forcing blacks to have abortions. This is obviously a completely different situation than abortion as we know it today, in which a woman chooses whether or not to have an abortion now, and then starts her family later in life, when her situation is more stable and conducive. The distinction between a woman choosing to control her fertility and the government choosing to limit her fertility is fundamental and people often seem to lose sight of that.
the rest here:
http://www.freakonomics.com/blog.php