In my opinion, the idea that Ancient peoples practiced infanticide is wrong. It certainly happened, but it could not have been frequent or the human race would have gone extinct. Consider how high infant mortality rates were. Either infant mortality rates were so low that exposing a few wouldn't imperil the survival of the community or infanticide did not or rarely occurred. Both things can not be true.

From a Pagan perspective, life is a gift from the Gods to the Ancestors handed down to us. Therefore, murder is a great evil. Human/child sacrifice can no more please the Gods than robbing a bank would please a banker. I am convinced much of these reports is simple slander or the exaggerated tales of deranged cults.

7123433
I'm not sure if they were under-represented, since it was usually included in detail as a staple of fables and myths and those aren't to be taken at face value. Did it happen? Yes, we have evidence of it. But we also have evidence showing that the demographics of babies that would have been killed with this method wouldn't be babies seen as "healthy" or "average". There's also the idea that when babies were demanded to be sacrificed, it was still considered a grave situation in many tales. Hera was a vindictive bitch and when she demanded for the latest kid of Zeus to die, it was seen as an example of godly wrath.

In Christian religion, having Isaac ready to be sacrificed was something that was not taken lightly. People also had many more children in the age than modern people do now. Last time I checked, modern people tend to have 2-3 kids (which makes sense) while ancient peoples often had 3 or more. Even though a child's death would have been something to mourn, there were still usually more children in a family. A modern family losing a child could risk their only heir if they lost a child today.

7123433
People do it today (abortion), so it’d be surprising if Ancient peoples didn't do it.