I was following along just fine until:
One way around this is to find some robust metric that most people would agree indicates guilt. One such measure, I believe, would be murder rate. If people in different cultures vary in the guilt they feel for committing murder, then this should hold them back and show up as a variation in the murder rate.
What? Is this an exercise in confounders? Could no longer suspend disbelief after that.
Related: The Psychological Diversity of Mankind, An African Folktale, many of the more interesting infanticide & abortion debates on this site
A fascinating post that however might need some background reading, most relevant material is linked in the article itself. I encourage reading up on the material.
Link to article.
Stories about changelings replacing babies and the recommended course of action being basically to expose the child is not a human universal, they are found only in European cultures. These rely more heavily on guilt and less on shame to regulate behavior than most other human societies. This may not be a coincidence. The stories look like they work as a ready made rationalization to reduce guilt from infanticide. Common problems often acquire common solutions like this.