i think because we live in a relatively morally advanced culture(*) it can be hard for us to realize that that ISN'T the way people just naturally think an act. culture needs to enforce the ideas that rape, assault, animal cruelty, etc are bad to the point that people think it's obvious. of course, this can lead to the issue where people think these morals are so obvious that they don't need to be enforced.
(*)a culture built on christian morality mixed with the ideas of individual liberty and the belief of innate human rights