It is even more creepy than how Ben Carson describes it. Margaret Sanger believed in birth control to keep the black population down; however, even Margaret Sanger opposed abortion for black fetuses. Even Margaret Sanger thought abortion was too barbaric for black people (see “Liberal Fascism” for the full explanation).
Her organization supported mandatory sterilization. Voluntary, if possible. Involuntarily, as necessary.
As far as abortion being too barbaric, please consider this quote from Eugenicist Sanger:
Many, perhaps, will think it idle to go farther in demonstrating the immorality of large families, but since there is still an abundance of proof at hand, it may be offered for the sake of those who find difficulty in adjusting old-fashioned ideas to the facts. The most merciful thing that the large family does to one of its infant members is to kill it.
Margaret Sanger, Woman and the New Race, (New York: Eugenics Press, 1920), chapter 5.