Government is a necessary good.
Here are some reasons why Christians oppose abortion.
1. We are anti-death as a matter of general principle. God throughout the Bible describes Himself as the living God. He is the Author of life. Christ raised people from the dead, He Himself rose from the dead, and defeated death for all who call on Him. Given what God is, how could we celebrate killing and death?
2. We are anti-murder. God said, "Do not commit murder" (Exodus 20:13, Deuteronomy 5:17). The Bible permits the taking of human life under strict circumstances. Human life may be taken when it is a punishment for an appropriate crime, such as rape or murder. Life may be taken in defense of innocent life, one's own or another. [This rule would allow ectopic abortion, to save the life of the mother. The removal of a miscarried baby is not an abortion.] Human life may be taken in an ethically justifiable war, which is a national extension of the self-defense rule. But God absolutely forbids all other killing of human beings. There is no question, scientifically, that the fertilized egg is a human being. God was angry that Simeon and Levi were cruel to animals (Genesis 49:5-7). How much angrier do you imagine God is about the killing of human beings?
3. We recognize God's sovereignty. Because of this essential worship-commitment, we reject the devilish idea that we are sovereign over ourselves. Whose body is this in which I live? God's. Whose life is this that I am living? God's. Don't I have the right to do with my body as I see fit? No. With reference to God and His laws, no one has ever had that right. God says, "Everyone belongs to Me." (Ezekiel 18:4). He says to Christians, "You are not your own; your body is a temple of the Holy Spirit; honor God with your body" (1 Corinthians 6:20).
Christianity is anti-death, anti-murder, and recognizes the universal authority of God. As a result, we oppose abortion.