Brian replies:
Fertilized eggs are potential people, or as you said, “what gets us to a person.” Ayn Rand has written about this distinction.

Consider the following in the context of giving a fertilized egg legal the protection of humans – from the paper (which includes references):

Significantly, natural or spontaneous abortion is a routine occurrence. Most fertilized eggs fail to implant; they are flushed out of a woman’s body. Due to the difficulty of detecting when a woman’s body rejects a fertilized egg, estimates of prevalence range widely. However, some researchers estimate that as many as 80 percent of fertilized eggs fail to implant.7 Even after a woman becomes pregnant with the implantation of the embryo, the risks of losing it by natural causes still hover around 10 to 25 percent.8 Nature is by far the greatest cause of death for fertilized eggs. (Notice that such natural deaths of fertilized eggs are not lamented, nor regarded as a public health crisis—not even by those who think of them as persons.) Thus Amendment 48 would ban forms of birth control that mimic the body’s natural processes. Also, as William Saletan observes, other activities that inhibit implantation include breast feeding, drinking coffee, and exercising.9 Would the defenders of fertilized eggs ban all women of child-bearing age from those activities, on the grounds that they risk killing human persons? Probably not—meaning that Amendment 48 would be selectively enforced.

Brian replies:
Fertilized eggs are potential people, or as you said, “what gets us to a person.” Ayn Rand has written about this distinction.

Consider the following in the context of giving a fertilized egg legal the protection of humans – from the paper (which includes references):

Significantly, natural or spontaneous abortion is a routine occurrence. Most fertilized eggs fail to implant; they are flushed out of a woman’s body. Due to the difficulty of detecting when a woman’s body rejects a fertilized egg, estimates of prevalence range widely. However, some researchers estimate that as many as 80 percent of fertilized eggs fail to implant.7 Even after a woman becomes pregnant with the implantation of the embryo, the risks of losing it by natural causes still hover around 10 to 25 percent.8 Nature is by far the greatest cause of death for fertilized eggs. (Notice that such natural deaths of fertilized eggs are not lamented, nor regarded as a public health crisis—not even by those who think of them as persons.) Thus Amendment 48 would ban forms of birth control that mimic the body’s natural processes. Also, as William Saletan observes, other activities that inhibit implantation include breast feeding, drinking coffee, and exercising.9 Would the defenders of fertilized eggs ban all women of child-bearing age from those activities, on the grounds that they risk killing human persons? Probably not—meaning that Amendment 48 would be selectively enforced.