The pro-choice agenda is not concerned with the fact that it is killing anything. Killing is not an issue for them. It is whose rights are of greater importance than another’s and for them it is the mother’s rights. Therefore, since the mother’s rights are greater, the mother can make the decision to kill the baby.
Pro-life people, on the other hand, basically say that the rights of both mother and child are more or less equal because all life is sacred.
The other part of this issue is that pro-abortion people generally believe that a person in the fetus stage is not an actual human being until it is viable outside the womb – meaning that it is not a person until it is capable of living outside of the mother by itself. This is about 7 or so months into the pregnancy I believe (anyone correct me if I am wrong please). Therefore, by having an abortion, they are nor killing a human being.