Honestly, I have kind of a mixed opinion on the subject:

Say, I impregnated my girlfriend. I would want the child to be put up for adoption. But since she is the one bearing the burden of pregnancy, I would agree and support her in the decision of an abortion.

However, in extenuating circumstances, such as rape, and drug abuse during pregnancy, I see no problem with it. While a child is a human being, it's usually born out of some type of love. If someone were to be raped, the child could cause psychological trauma to the mother, probably for the rest of her life. If the mother of the child was heavily into drugs, causing serious health problems for the child, I think it would be better for it to not be brought into the world with the burden of a terrible sickness or dysfunction in the body.