We may not see any moral harm done to the fertilized egg itself in its destruction. But we may still want to call it a "person" for in a strategy of protecting real persons.
We see the danger to real persons, even those outside the womb that pro-choicers see as persons, in too many "pick a person points" on the slippery slope.
The pro-lifers (I include myself as partly pro-life), have started a perception shift in society concerning personhood. Finding the next bright line seems too hard to agree on, hence some pro-lifers picking conception. That umbrella certainly protects all persons, and saves time and resources.
I think there is ample scientific evidence for that choice as well as being logically and ethically defensible. Appropriate and reasonable application of Occam's Razor leads us to that point anyway.
If you did an unofficial survey of your friends and family, to see how many actually realize that the embryo builds its own placenta, that the mother doesn't build the placenta nor the other tissues and organs of the individual in utero ... if you did such a survey, I would bet the number of persons you could find who know the actual scientific facts would be less than ten percent.
The original purpose of this essay (I have this on good authority, that the author intended this) was to connect the meaning of the protocol defining 'aliveness' when contemplating organ harvesting, to the advent of individual human life, to show the embryo fits the protocol standard for 'aliveness' as an integrated functioning whole organism and is thus as much a human being as one being considered for organ harvesting but who evidences the standards for still being an alive individual and thus not to be harvested from. How do you feel about that notion?