If a human being is not as intelligent, if it can't do what others can do, then it has no rights. That's the argument. The unborn doesn't look like other real persons and it doesn't act like other real persons, therefore it is not a real person. My point is, being a real person is not a look like or an act like kind of thing. It is a be like kind of thing.
Human beings are persons by their nature.
This was an argument that Lincoln made regarding the Lincoln-Douglas debates against slavery. If personhood is gradual and admits to degrees, then human rights based on personhood are gradual and admit to degrees. If any human being can be disposed of simply because he or she doesn't look just right or can't do what others can do, then the world is only safe for the perfect. That's what this argument says. That is precisely what the personhood argument entails.