What you would say if your interest was in accuracy would be, "the idea that women are even using abortions as their primary source of birth control is a myth, period". Unless a woman choses abortion because the premature death of the fetus, she is indeed using it as birth control, as should be her right. There's no need to go through logical contortions to explain or justify abortion, it is health care, it is a form of birth control, and it is a woman's right to use.