More accurately, the question is whether it is something that you can be in the future. Indeed, that's the only question that matters. Infants are often less intelligent than adult animals when born. And it is by no means a given in human nature that killing an infant is murder, given the prevalence of infanticide throughout history though the modern day. That said, we've decide that infants are full humans and to kill one is murder. Why? I think for much the same reason why a key element in defining "clinical death" is whether the patient can ever recover. We look the the future. And must.
Indeed, murder is not wrong for the immediate pain it causes. Murder may be performed painlessly and extreme torture can be inflicted yet murder is considered the ultimate "capital" crime. Why? Because it robs a living being of its future in a way that no human can restore. And it is that awareness of a lost future that makes us grieve more, for better or worse, for a young child two dies than an elderly person in a nursing home at the twilight of their life. And it is that awareness of the absence of a future that allows us to consider the perminently brain dead that will never recover "clinically dead" and which allow some to accept that killing the terminally ill could be considered "mercy".
Science fiction is full of examples of the detachment of the present capacity of an individual from their "personhood". The original Star Trek series had an expisode where two crew members were reduced to foam blocks. One was crushed while the other was restored. The implication was clear to any who watched it. The crewmember who was crushed as a foam block was "murdered" because they could no longer be restored. Though is was fantasy, the scene would have had no emotional impact if, looking at the inert block of foam, the audience simply concluded "no brainwaves, no heartbeat, and no conscious so no murder was committed."
As to the hall of life, the key question is missing from this essay. Why does the author (or their father) wander from "yes" to "probably" and eventually to "no"? By what criteria are those transitions made? By how the fetus "looks"? The truth is that there are no non-trivial criteria that will let you declare a human fetus, or even a human infant, a "person" while denying that status to my pet cats. It is only looking at what something can become, if given time to grow or recover, that we can develop criteria consistent with how we define persons from the animals and the clinically dead in every other case.