I decided to reprint this article in whole to give readers the full context of what is being said. To see it in the context of its on-line publication, St. Louis REVIEW, please visit the link at the end of the article.
Before the Cross | Good Catholics cannot be pro-choice; The Fifth Commandment demands respect for life as God's most precious gift.
By Archbishop Robert J. Carlson
[Emphases & comments are mine.]
God's law in the Old Testament is clear and unambiguous: You shall not kill. Jesus is even more demanding: Every one who is [unjustifiably] angry is liable to judgment.
Sins against the Fifth Commandment are easy to commit. Any time we think, speak or act out of anger or hatred or jealousy or revenge, we abuse God's commandment that we respect His most precious gift, the gift of life — especially human life. [This is a good reminder for our daily behavior.]
Human life is sacred because, from its beginning until its natural end, it involves the creative action of God. The Fifth Commandment forbids direct and intentional killing as gravely sinful. God alone is the Lord of life. No one has the right to end arbitrarily what God has begun, and sustained, through the gift of His love.
In the account of Abel's murder by Cain (Genesis 4:8-12), Scripture reveals the presence of anger and envy in humankind, consequences of original sin, from the beginning of recorded history. God declares this as wicked, and He asks the question to be answered over the ages: "What have you done?" Today this question is asked not only of those who kill someone, but also of those responsible for violence, anger, hatred and vengeance in any form.
It is a shame that there are so many violent words expressed between members of the same family day in and day out. Anger and intolerance are also pervasive in our Church and in society. Such attitudes are destructive and sinful. They are of the Evil One and not of God.
The Fifth Commandment does not stop someone from self defense, because someone who defends his or her own life is not guilty of murder. Legitimate defense can be not only a right but also a grave duty for someone responsible for another's life, the common good of the family or the security of a nation. We risk our lives to protect ourselves and others because we value human life and freedom so dearly. They are gifts from God that we are bound to cherish and defend.
Since the first century, the Church has addressed the moral evil of abortion and the killing of a defenseless baby in the womb. People who are casual about the sin of abortion and who choose to view it as a political issue rather than the serious moral issue that it is are guilty of violating the Fifth Commandment. You cannot be "pro-choice" (pro-abortion) and remain a Catholic in good standing. That's why the Church asks those who maintain this position not to receive holy Communion. We are not being mean or judgmental, we are simply acknowledging the fact that such a stance is objectively and seriously sinful and is radically inconsistent with the Christian way of life.
The Fathers of the Second Vatican Council said, "God, the Lord of life, has entrusted to men the noble mission of safeguarding life, and human life must be protected with the utmost care from the moment of conception: Abortion and infanticide are abominable crimes" ("Gaudium et Spes," No. 51.3). That's why formal cooperation in an abortion constitutes a grave offense. The Church attaches the canonical penalty of excommunication to this crime against human life (see canons 1398,1314, and 1323-1324).
The Fifth Commandment also directs us to work for justice and peace — avoiding war whenever possible — and to limit the use of capital punishment to the most extreme (and rare) circumstances required to protect human life. Only God has the right to take the life of another human being. When we take that action into our own hands — in self-defense or in defense of others — we had better be sure that all other options have been exhausted!
In addition, euthanasia or deliberately taking of the life of someone who is sick, dying, disabled or mentally ill is morally unacceptable. The Church calls for the ordinary care owed to a sick person, but medical procedures that are burdensome, dangerous or extraordinary are not necessary. If you are unsure about the moral implications of health care procedures that are being proposed for someone you love, contact your pastor or the archdiocese's Respect Life Apostolate. They will be happy to help you consider approaches that are in accordance with our Church's teaching about care for those who are sick or dying.
Taking proper care of our health, respecting others and showing respect for the dead are all matters covered by the Fifth Commandment's demand that we reverence God's most precious gift — human life. - http://stlouisreview.com/article/2010-07-06/cross-good-catholics
This article is part of a series Archbishop Carlson has been writing on the Ten Commandments in his Before the Cross column.
Carlson is well known for taking a strong stand on life issues. In 2003, then-Bishop Carlson ordered abortion advocate Tom Daschle to stop calling himself Catholic. Here are some related writings.
Preparing For the Nov. 4 General Election 
Archbishop Carlson at St. Louis installation: ‘We will never compromise our commitment to life’ 
Is ProChoice Really Pro Choice? 
image - http://archstl.org/archstl/page/archbishop-robert-j-carlson