“Personhood is not a separate, added quality that gives human beings significance. It is a property that is essential to being human. Humans are personal beings. It’s part of an inseparable package. For example, an essential part of being a sphere is to have volume. A sphere without volume is not a sphere, but a circle. All spheres have volume. In the same way part of what being human entails is being a personal being.”
https://www.str.org/blog/are-you-a-person
“Personhood is not a separate, added quality that gives human beings significance.”
That argument is somewhat tautological. In this context “person” and “human being” are two terms for exactly the same thing. So what have you proven? The important question is when, exactly, does a human egg become a human being? Is it when it becomes “viable”? When it’s “inevitable”? When it’s capable of free will? When it looks like a person? When it looks too cute to harm?
According to US law, when most of the head of a developing human “something” is outside of its mother’s body, it suddenly, mystically, becomes a human being, endowed with full human rights. This arbitrary and quasi-religious definition is sanctified as “settled law”. That’s sure to cause bitter problems, and it does.