In my previous article on Personhood, I explained that what makes us “persons” (if you must use the term) is our inherent nature as rational, moral agents. While I tend not to focus on personhood arguments unless the topic is broached by the other person, I can only see one reason for disqualifying the preborn from personhood: in order to justify killing them. Any definition for personhood given by a pro-choice advocate works equally well to disqualify some born people from that same status (most notably, infants). But most pro-choice people would not follow their definitions to the logical conclusion and support infanticide.
The best way to see personhood is based on what the nature of personhood is, and on who qualifies as agents who have that nature (which includes the preborn). I will now turn to arguments against fetal personhood. I will address four different arguments: Speciesism, Gradualism, Threshold Arguments, and Functionalism.
First I’ll address Peter Singer’s charge that the pro-life position is a speciesist position. Frank Beckwith explains, “Just as racism is arbitrary because color and ethnicity are irrelevant to assessing a human being’s intrinsic worth, those who charge pro-lifers with speciesism argue that preference for the species Homo sapiens is just as arbitrary.” 
However, this argument misses the point entirely. The pro-life position is not grounded in the fact that human beings belong to the biological species, Homo sapiens. The pro-life position is grounded in the nature of human beings. Beckwith continues, “However, this charge is a red herring. For the pro-life position is based on the personal nature of human beings and the presence of that nature from the moment a human being comes into existence regardless of whether it has the present exercisable capacity for, or is currently engaging in, personal acts.”  Because human beings are intrinsically valuable as rational, moral agents, and because they have a personal nature, they are intrinsically valuable. And because the preborn share this human nature when they come into existence, they are equally intrinsically valuable.
Christopher Kaczor adds, “...even if speciesism is ethically problematic, a commitment to the dignity of all human beings does not involve a denial of dignity to any other class of non-human beings simply because they are not human. Defenders of the dignity of all human beings need not believe, and characteristically do not believe, that only humans have dignity.”  As I mentioned in my previous article, simply considering someone a person does not automatically disqualify non-persons from dignity or from possessing a right to life.
In fact, the very fact that humans are uniquely valuable means that racism and sexism are inherently morally wrong because race and gender are arbitrary distinctions. It’s wrong to discriminate against someone based on race and gender because simply being female or of a different nationality has no bearing on someone’s capacity as rational, moral agents. But since that is what makes us valuable, then if another species does not share that inherent nature with us, they are not on par with us as far as intrinsic worth (but it may still be wrong to kill them for other reasons).
Clearly, the pro-life position does not entail speciesism. 
This is the argument that pro-life philosopher Trent Horn referred to as Golden Retriever Reasoning.  This position essentially states that the unborn don’t have the same value that we do, but they do have some value, just like dogs do. It would be wrong for me to kill my neighbor’s Golden Retriever, not because he’s as valuable as humans but because he belongs to my neighbor. Additionally, you shouldn’t just kill them for a trivial reason, but if circumstances get very tough, then you are justified in killing them.
But as Trent points out in the video, this doesn’t account for why we treat the unborn as no different than infants in some situations (for example, in some states if you kill a wanted unborn child you are charged with murder, not animal cruelty, such as when Scott Peterson killed his pregnant wife and unborn child in California several years ago; he was charged with two counts of murder). In fact, many pro-choice people do treat the unborn as babies if they’re wanted.
We don’t become “more human” by developing further, we just develop more of the traits that humans possess. Similarly, we don’t become “more of a person” by developing further, we just develop the capacity to perform the functions that persons can perform.
So the Gradualist position just doesn’t account for why abortion should be available, especially on demand as we currently have it in the United States now.
Threshold arguments are similar to Functionalist arguments in that they essentially state that you don’t become valuable until you pass a particular “threshold” of an ability that they deem as morally relevant to your right to life. For example, fetuses in the third trimester have a limited degree of consciousness, but not enough to grant them a right to life like people outside the womb.
A problem with this argument is almost always immediately apparent: they can never articulate just how much of a particular quality is needed to make you valuable. It is usually an ad hoc requirement. As pro-life advocate Josh Brahm points out, pro-choice people often try to draw a line on the spectrum of functionality that makes one a person. But if you define it too strict, then you disqualify infants. Conversely, if you define it too broadly, then not only do you include late-term fetuses but also many animals, like squirrels.
There’s just no reasonable place on the spectrum of functionality that isn’t simply an ad hoc requirement specifically to disqualify the unborn from personhood. More than that, however, if it can be shown that it’s not our presently-exercisable capacity to perform a function that makes us valuable, then it would seem that threshold arguments would automatically fail as a result.
This is the argument most commonly supported by pro-choice advocates. Pro-choice philosophers (e.g. David Boonin, Peter Singer, and Mary Anne Warren) argue that the unborn are not persons because they can’t perform many of the same functions as you and I can. More than that, pro-choice philosophers differ on what it is that makes us “persons,” so they have different criteria as to when the unborn become valuable:
David Boonin believes that we don’t have a right to life until cortical activity begins in the brain. This is because cortical brain activity is needed for an entity to have desires, so before the entity can be said to possess desires, then you are not harming anything because you are not frustrating anyone’s desires to live.
Peter Singer argues that self-awareness is what makes one valuable, self-awareness being the ability to perceive of oneself and to recognize oneself as existing through time. Since you have no future plans to be thwarted and you don’t value your life, it can’t be said that you are being harmed if you are taken out of existence.
Mary Anne Warren has five different criteria for personhood, and while she concedes that you don’t need all five to be a person, if you possess one or two (which the unborn do not), then you may possibly possess personhood. But if you don’t possess one of Warren’s criteria for personhood, then you definitely are not a person.
Some philosophers, like Peter Singer, follow their arguments to their logical conclusion and support infanticide, since infants are fundamentally no different than late-term fetuses. Other philosophers, like Mary Anne Warren, don’t. Rather than reject her criteria for personhood, Warren take the ad hoc approach. She argues that since infants are close enough to being persons, we should consider them persons rather than support infanticide (though she would say infanticide if the child is severely deformed may be permissible).
In the future, I will write article on where exactly these different pro-choice philosophers stand and why their arguments ultimately fail, but for now I’ll just write a brief rebuttal of the Functionalism criteria in general.
So is it a particular function that you can perform that makes you valuable? There are two types of capacities we can be said to have. One is the presently-exercisable capacity, and the other is the radical, or inherent, capacity. If you have the presently-exercisable capacity to perform a function, that means you can perform it now (such as you have the presently-exercisable capacity to read). The inherent capacity is one in which you can’t presently exercise, but you can or will do it if you develop enough or learn how to do it (infants have the inherent capacity to read). I also have the presently-exercisable capacity to speak English. I have the inherent capacity to speak German, which would become presently-exercisable if I ever decide to learn the language.
The problem with requiring a presently-exercisable capacity to perform these functions is that we occasionally lose the ability to perform these functions, and we once lacked the ability to perform these functions.
For example, what of Singer’s argument that self-awareness is what makes us valuable? We begin life out of the womb without being self-aware. We don’t become self-aware until about sixteen to eighteen months after we’re born. So if that’s your criterion, then you would have to support infanticide. Now, if you’re like Peter Singer, that’s not a problem (because he bites the bullet). But if you can’t bring yourself to concede infanticide is morally permissible, then you must reject this criterion as one that makes us valuable.
So what if you’re a fan of Peter Singer? Well, we also know that we lose the capacity for self-awareness at times. We are not self-aware when we fall asleep, enter a reversible coma, or go under general anesthesia before surgery. So is it morally permissible to kill us for any reason during those times? Yes, if we must be self-aware to be valuable.
But, you might respond (as Peter Singer does), if you fall sleep, go under anesthesia, or enter a reversible coma, you once were self-aware. So as long as you once exhibited the capacity for self-awareness, it would be wrong to kill you. Frank Beckwith offers the following thought-experiment:
“Suppose your Uncle Jed is in a terrible car accident that results in his being in a coma from which he may or may not wake. Imagine that he remains in this state for roughly two years and then awakens. He seems to be the same Uncle Jed that you knew before he went into the coma, even though he’s lost some weight, hair, and memories. Was he an [intrinsically valuable human being (IVHB)] during the coma? Could the physicians have killed Uncle Jed -- the living organism we refer to as ‘Uncle Jed’ -- during that time because he did not exhibit certain functions or have certain present capacities? If one holds that IV depends on capacities that are immediately exercisable, it is difficult to see why it would be wrong to kill Uncle Jed while he was in the coma. Yet it would be wrong, precisely because Uncle Jed is identical to himself through all the changes he undergoes and that self, by nature, has certain basic capacities.
“Consequently, the [Anti-Equality Advocate] cannot reply by arguing that Uncle Jed’s life was intrinsically valuable during the coma because in the past he functioned as an IVHB and probably will do so in the future. For we can change the story a bit and say that when Uncle Jed awakens from the coma he loses virtually all his memories and knowledge including his ability to speak a language, engage in rational thought, and have self-awareness. He then would be in precisely the same position as the standard fetus. He would still literally be the same human being he was before the coma but he would be more like he was before he had a “past.” He would have the basic capacities to speak a language, engage in rational thought, and have self-awareness, but he would have to develop and learn them all over again for these basic capacities to result, as they did before, in present capacities and actual abilities.” 
So it really seems that it’s not our present capacity to perform a function, but our inherent capacities, that make us human. This way we can lose our present ability to function but still be seen as a valuable human being that is wrong to kill, whether in the embryonic stage or in a case like Uncle Jed (whom a Functionalist would have to admit would not be wrong to kill while he’s in the coma).
Additionally, as philosopher Stephen Schwartz points out, claiming that one must perform functions that make one a person before one can be considered a person commits the fallacy of confusing cause and effect. Philosophers like Singer, Boonin, etc., confuse functioning as a person with being a person.  You must be a person first before you can function as one, just as you must be a human first before you can function as one.
Finally, what of people who fail to develop a capacity that other human beings can perform, like the seriously disabled? Singer would admit that they are not persons, but is it truly permissible to kill them? As Christopher Kaczor would note, just because a human being or person fails to develop a capacity that makes one a “person” (say because of a disability), he is still a person because he still has the inherent capacity to fulfill these functions. If a dog loses the ability to bark, does he cease to be a dog? If a person becomes blind, does he cease to be a “person” or “human,” even though this is a function that human people can perform? Of course not.
It seems that the best explanation for what makes us valuable human persons is not the functions that we develop to perform, but the functions that are in our inherent nature as human beings to perform. The unborn share our common human nature, and the inherent capacities that make us valuable as human persons.
 Frank J. Beckwith, Defending Life: A Moral and Legal Case Against Abortion Choice, Cambridge University Press: Cambridge, New York, 2007, p. 161.
 Ibid, pp. 161-162.
 Christopher Kaczor, The Ethics of Abortion: Women’s Rights, Human Life, and the Question of Justice, Routledge, 2007, p. 92.
 In fact, Don Marquis mentions in his article Why Abortion is Immoral, that if his Future-Like-Ours argument succeeds, it likewise avoids the charge of speciesism because if animals had the same type of future we do, it would also be wrong to kill them.
 Trent starts to talk about this at about fifteen minutes into the video.
 Beckwith, Defending Life, p. 135.
 Stephen D. Schwartz, “Personhood Begins at Conception” from The Abortion Controversy, ed. by Louis P. Pojman and Frank J. Beckwith, (Wadsworth Publishing Company, 1998, p. 260.