You know whats funny about this whole idea.
Is that we are even arguing about it.
Lets say in the whole world only your family exists. And mama and papa just meh we dont want another kid, lets scrap it. There will be no one to judge them or care about this shit.
But if it was one's living mother, brother or aunt that is somehow killed everyone in tribe would care and smash the murderer dead with a stone.
Legit infanticide was a socially acceptable form of birth control across asia for the longest time. And a more covert infanticide is happening in modern day Africa to this day - it is normal in many african countries to refuse to feed your kid after weaning it off the tit. So at 1.5-3 years of age children are expected to scavenge for their food on their own like stray dogs. This is the main reason for huge child mortality and malnutrition in africa btw, if adults shared food with kids it would instantly decrease because they do have plenty of food, there is food everywhere in africa. I dont even want to mention all the paganic rituals for murdering children that were omnipresent in the world before modernity.

So a tldr is that barring some autists, most of humanity naturally gravitates towards not giving a shit about babies and not considering them a valid part of "humanity". Its is not murder because no one cares if it dies.
Caring about fetuses on top of all of that, is completely unnatural christianity induced hysteria, so a form of mental illness. But of course that is not really it. Its not about fetuses or babies at all, all of it is just rhetorics for pressure on women and general pressure for peasants to produce new taxpayers. Now the people that genuinely believe the whole murdering babies thing are indeed just mentally ill.