Historically, abortion has never been considered morally permissible. In the early church, authors like Athenagoras, Tertullian, Hippolytus, John Crysostom, and others listed it among other serious, grave sins. In fact, up until the last 40 years, no serious Christian group would have ever considered abortion moral. Pope John Paul II wrote an encyclical on how it, euthanasia, death penalty, and other threat to life, are having effects in this world. I’d encourage anyone who doesn’t understand the Catholic Church’s consistent ethic of life to read this document called The Gospel of Life.
I found two quotes from other sources that have helped as I approached this question. The first comes from Pope Benedict XVI, “In the radical version of the Enlightenment’s individualistic tendency, abortion appears to be one of the rights of freedom; a woman must be able to have control over herself. She must have the freedom to bring a child into the world or rid herself of it. She must be able to make decisions concerning herself, and nobody else, so we are told, can impose upon her, from without, any ultimately binding norm. It is a matter of the right of self-determination. But, in an abortion, is the woman actually making decisions that concern herself? Is she not in fact making a decision about someone else – deciding that this person should be allowed no freedom, that she sphere of freedom – his life – should be taken away because it is in competition with her own freedom? And thus we should ask: What kind of a freedom is this that numbers among its rights that of abolishing right from the start?”
(Joseph Cardinal Ratzinger, Truth and Tolerance: Christian Belief and World Religions pps. 245-246 c. 2004 Ignatius Press)
Also, from Mother Teresa, "America needs no words from me to see how your decision in Roe v. Wade has deformed a great nation. The so-called right to abortion has pitted mothers against their children and women against men. It has sown violence and discord at the heart of the most intimate human relationships. It has aggravated the derogation of the father's role in an increasingly fatherless society. It has portrayed the greatest of gifts -- a child -- as a competitor, an intrusion, and an inconvenience. It has nominally accorded mothers unfettered dominion over the independent lives of their physically dependent sons and daughters" And, in granting this unconscionable power, it has exposed many women to unjust and selfish demands from their husbands or other sexual partners. Human rights are not a privilege conferred by government. They are every human being's entitlement by virtue of his humanity. The right to life does not depend, and must not be declared to be contingent, on the pleasure of anyone else, not even a parent or a sovereign."
(Mother Theresa, “Notable and Quotable”, in Wall Street Journal, 2/25/94, p. A14)