As abortion takes away the fetus' right to life. If we assume that a fetus has a right to life, then we must assume that this takes away the mother's right to life, liberty, and pursuit of happiness - two entities occupying one body means that if one entity exercises control over their rights, it would nullify the other's. During pregnancy, mothers tend to forego their own rights in order to allow a fetus to gestate unless it interferes with their very own health. If a mother chooses not to forego her rights to life, liberty and pursuit of happiness - why should she have to carry the term? This goes especially in the case of failed contraception. If pregnancy didn't involve the 9 months of carrying a child and the pain of childbirth, then maybe the adoption argument would work - but until such technology exists, the abortion debate will continue. A mother carrying a normal pregnancy to term does not forgo her right to life. The flaw with your argument is that while there will be some conflicting rights when two entities occupy the same body, it isn't always the case. The only way the mother's right to life is being threatened by pregnancy is if carrying the child to term will result in her death; an abnormal pregnancy in which case abortion becomes a morally acceptable medical procedure.