Why do so many Christians believe that abortion is a sin?

Yes, abortion is wrong. The Lord has said, "You shall not murder," (Exodus 20:13). The life that is growing within the mother is a child, a baby. The Bible looks at the life in the womb as a child.: Exodus 21:22 says, "And if men struggle with each other and strike a woman with child so that she has a miscarriage, yet there is no further injury, he shall surely be fined as the woman's husband may demand of him; and he shall pay as the judges decide,"