Introduction

There are some people who claim that the Church began to oppose abortion only recently. This is simply not true. The Catholic Church has always opposed abortion, and there was never a time in history when it was tolerated. Everyone concedes abortion kills something. The crucial question is “what is killed?”. If the unborn are not human, no justification for abortion is necessary. However, if the unborn are human, no justification for abortion is adequate. As Catholics, we believe human life begins at conception. From that moment, the complete genetic blueprints are there, the DNA is determined, the blood type is determined, the sex is determined, the set of fingerprints that nobody else has are already determined. We hear critics describe the unborn as a lump of indiscriminate cells, and not recognizable as human. The unborn does not look like a baby in the same way that a baby does not look like a teen, and a teenager does not look like a senior citizen. The unborn baby looks exactly the way human beings are supposed to look at that stage of development. Don’t be fooled by the culture of death.

Catechism
Since the first century the Church has affirmed the moral evil of every procured abortion. This teaching has not changed and remains unchangeable. Direct abortion, that is to say, abortion willed either as an end or a means, is gravely contrary to the moral law: You shall not kill the embryo by abortion and shall not cause the newborn to perish. God, the Lord of life, has entrusted to men the noble mission of safeguarding life, and men must carry it out in a manner worthy of themselves. Life must be protected with the utmost care from the moment of conception: abortion and infanticide are abominable crimes.
- Catechism of the Catholic Church, 2nd ed., (1997), n.2271
Formal cooperation in an abortion constitutes a grave offense. The Church attaches the canonical penalty of excommunication to this crime against human life. "A person who procures a completed abortion incurs excommunication latae sententiae, by the very commission of the offense," and subject to the conditions provided by Canon Law.
- Catechism of the Catholic Church, 2nd ed., (1997), n.2272
Scripture

Ex. 20:13; Deut. 5:17; Mt. 19:17-19 – Thou shalt not kill. This is a clear and direct teaching against abortion.

Ps. 138:13-16; Jer. 1:5; Isa. 49:1,5; Gal. 1:15 – Before you were born, God knew you. You had personhood.

Lk. 1:41-44 – Elizabeth’s infant leapt for joy in her womb. The unborn John was filled with joy at the presence of Christ.

Jn. 11:25; Jn. 14:6 – God is Life. An attack on life is an attack on God.

1 Cor. 3:16-17 – Your body is a temple to God. Abortion defiles Gods temple.

1 Cor. 6:20 – Only God is entitled to determine the end of one’s life. Suicide, murder, and abortion are mortal sins.

Tradition & Fathers
"You shall not kill by abortion the fruit of the womb and you shall not murder the infant already born."
- Didache Apostolorum, 2:1 (A.D. ~90)
"To prevent birth is anticipated murder; it makes little difference whether one destroys a life already born or does away with it in its nascent stage. The one who will be a man is already one."
- Tertullian of Carthage, Apology (A.D. 160-240)
"Women who were reputed to be believers began to take drugs to render themselves sterile, and to bind themselves tightly so as to expel what was being conceived, since they would not, on account of relatives and excess wealth, want to have a child by a slave or by any insignificant person. See, then, into what great impiety that lawless one has proceeded, by teaching adultery and murder at the same time!"
- St. Hippolytus of Rome, Refutation of All Heresies (A.D. 170-235)
"But the man, or woman, is a murderer that gives a philtrum, if the man that takes it die upon it; so are they who take medicines to procure abortion; and so are they who kill on the highway, and rapparees."