That kind of sounds like the Freakonomics view that abortion reduces crime. I think there are too many variables to say that it does.
http://www.freakonomics.com/2005/05/15/abortion-and-crime-who-should-you-believe/
What I was asking for is quite objective.
Basically, since Roe v. Wade, how many babies have been aborted, broken down by race? Then, if they had lived to adulthood, if the typical number themselves had children there would be even more people.
Though the majority of aborted babies were white, still the number of aborted black babies was significantly higher than the percentage of the American population that are black.
In turn, this means that there would be many more black Americans than there are right now. Right now, 12% of Americans are black. Were it not for Roe v. Wade, it might be 13, 14, or 15%.