The Church recognizes that the obligation to protect unborn human life rests on the answer to two questions, neither of which is private or specifically religious.
The first is a biological question: When does a new human life begin? When is there a new living organism of the human species, distinct from mother and father and ready to develop and mature if given a nurturing environment? While ancient thinkers had little verifiable knowledge to help them answer this question, today embryology textbooks confirm that a new human life begins at conception (see www.usccb.org/prolife/issues/bioethic/fact298.shtml). The Catholic Church does not teach this as a matter of faith; it acknowledges it as a matter of objective fact.
The second is a moral question, with legal and political consequences: Which living members of the human species should be seen as having fundamental human rights, such as a right not to be killed? The Catholic Church’s answer is: Everybody. No human being should be treated as lacking human rights, and we have no business dividing humanity into those who are valuable enough to warrant protection and those who are not. This is not solely a Catholic teaching, but a principle of natural law accessible to all people of good will. .... Those who hold a narrower and more exclusionary view have the burden of explaining why we should divide humanity into those who have moral value and those who do not and why their particular choice of where to draw that line can be sustained in a pluralistic society. Such views pose a serious threat to the dignity and rights of other poor and vulnerable members of the human family who need and deserve our respect and protection.
While in past centuries biological knowledge was often inaccurate, modern science leaves no excuse for anyone to deny the humanity of the unborn child. Protection of innocent human life is not an imposition of personal religious conviction but a demand of justice.
Hurray! No more "personally opposed, but ...."