When Abolitionists posit that all human beings are endowed by their Creator with certain inalienable rights, among which is the right to life, these Abolitionists are not just positing their mere opinion, rather, they are leaning on the word of God. What the framers of the Declaration of Independence puts it in the positive, "that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life...", the word of God puts it in the negative, "you shall not murder (Exod 20:13)."
Why then does the law of God prohibit the murder of the innocent? It is because God had created man in his own image (Gen 1:26). To destroy an innocent man is to offend the God in whose image man is made. This is why God says that the only just punishment for murder is capital punishment: "Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image (Gen 9:6)"
