Morals are cultural. The Aztecs religion (along with many other historical ones) included human sacrifice to the Gods. When the Spanish conquered them, they stamped out the practice and converted the population to Christianity.
What was one of the most important part of the culture of one group and in certain contexts massively increased social standing was abominable to another.
In a modern context the pro choice - pro life battle exists where one side considers the bodily autonomy of the woman as having the greatest importance and the other side considers the safety of the unborn child as having the most importance. While there is a lot of grey area in between the two positions, at the most extreme both sides consider the other to be evil.
Who has rights, the mother or the child? The answer is neither. In the absence of a legal framework the mother has the power imbalance over the child. Where laws exist protecting the unborn child the state acts to protect the child shifting that power balance
