Why are most Catholics pro-life?

The Catholic church is an institution that has absolute rules on moral issues. One of these is abortion. They use Biblical passages such as Jeremiah 1:5 'Before I formed you in the womb, I knew you' and Genesis 1:27 'let us make mankind in our image'. These are the literal words of God so hold the highest authority possible. From this Catholics have created the concept of the sanctity of life, this is that all human life is special to God. Therefore taking any human life is to commit murder- which is to break one of the 10 commandments. Therefore abortion is wrong because it involves killing a human, or a potential human.