There is no such thing as an unwanted child. Even if the mother cannot support the child, there are extensive waiting lists for families looking to adopt.
At any given moment, there are more than 1.5 million American families on the waiting list to adopt a child. These couples are waiting for a child to join their family and have love to give. Why would we allow abortions when there are so many parents waiting for a child? 
Even if the biological mother doesn’t want the child, there is no shortage of families who will love and cherish it. Killing a life form when so many people want a child of their own and are looking to adopt is an act of selfishness and should not be permitted.
Putting a child up for adoption is a huge undertaking. It requires the mother to carry the child in her womb for nine months, during which time a bond is created with the child. As a result, many mothers who have given a child up for adoption often suffer intense feelings of loss which last for the rest of their lives. Many women would prefer to abort the foetus than being forced into completing the full term the pregnancy. Partly, this is because although there is a large number of families hoping to adopt an infant, children from ethnic minorities often languish in foster homes and grow up in social services. Adoptive parents do not adopt babies of colour at the same rates they do young, white children. Why would you force a mother to go through an unwanted pregnancy, only for the child to end up in social services? If a pregnant woman chooses to go through the pregnancy and relinquish her child, that is a noble and selfless decision. But that is her decision to make. Adoption is always an option, but it should never be the ONLY option and it is certainly not her duty.
[P1] There is a surplus of prospective adoptive parents. [P2] Therefore, abortion is never necessary. [P3] If adoption is always an option for mothers who cannot raise their child, abortion should be prohibited.
[Rejecting P3] Adoption should not be a mother's duty. It should be her choice given the consequences.