I think some of the discussion here has gotten a bit heated, so I would like to ask a few questions and try to clarify some positions and bring out some common understanding.
1. Scientifically, we already know that arguments which state a Fetus is not a Human are false. We also know arguments which claim they are not alive are false. Humans at stages of development are alive. However, one must logically ask oneself whether the fact that something is alive merits the concept of rights. Life itself does not guarantee anything; everything has some subjective value relative to something else, but we have to come up with some type of universally applicable value assessment. To this, I ask:
1. What makes Humans valuable? In essense, what separates us myriad other animals to which we don't ascribe the same level of rights? Why do we treat them differently? Is it that we are alive? That cannot be, since saying so would form a contradiction with our treatment of other animals or even the vegetative. We need to come up with something that is consistantly applicable. Personally, I think there are two major, basic elements which and give Humans value and that warrant rights.
1. Sentience (suffering and happiness)
2. Existence of the Self
--- Self-Awareness (the recognition of oneself as a continuing entity)
--- Rational Autonomy (ability to express and act upon preferences)
In essense, the importance of any Human obviously rests mind or personality, not merely in the body. Let us do a thought experiment to clarify the value of the mind over the value of the medium of transport.
1. We have a Cow and a Human. Which one has moral personhood? The Cow or the Human? Naturally, you would say the Human, because the Human meets the above criteria for human rights. However, say one day we are able to replace the mind of the Cow by putting it into the body of the Human. We then take the mind of the Human and put it into the cow. Now, the Cow body is the Human personality/mind and the Human body is the Cow/mind. Now who hs the value of moral personhood? If the value of an individual is the fact that he is an individual with a self-conscious mind, does it matter in what physical form that Human is? Obviously, the Human still exists in moral personhood regardless of the physical appearance. The cow mind is still a cow mind. As such, we can see that both the qualifers "life" and "body" are irrelevant to discussing moral personhood.
2. After determing what items make creatures valuable, but humans in particular, we must ask ourselves, "What is the nature of the fetus?" Well, what is the fetus at early and late stages? Does the fetus have the above characteristics that makes a human valuable? When does a being generally attain these characteristics?
3. Then we must ask ourselves what we should do if said being in question does or does not have the necessary elements of Human value. Well, do we attach rights and privlidges stemming from existence of the above "Moral Personhood" criteria, even if said individual does not meet those criteria?
A. First, we must also make a difference among entities that have never met said criteria, those that had, but temporary reliquished criteria, and entities which will never meet said chriteria. It would be absurd to attribute rights to entities which don't have and have not yet attained the criteria of moral personhood as much as it would be absurd to attribute rights to those who have attained said criteria, but lost ability to meet criteria permanently. This ties into another concept to think about: actualization-potential.
4.
A. Does the fetus have the potential to attain moral personhood? Yes. It does. Unlike many other organisms, Humans do have the basic biological framework to reach all the characteristics of moral personhood, given that nothing happens to prevent that. However, the concept of "potential" is very tricky ethically. Not all potential is on the same level. Potential matters in terms of degrees and stages, but not absolutely. For example, when dealing with entities which have never attained moral personhood, it is irrelevant whether or not the being will sometime in the future exist in moral personhood. There is a potential for a being to exist, but no being yet exists. It's absurd to treat a fertalized egg the same same as a newborn. They simply are not of the same value. We cannot fairly attribute rights to a being which isn't and never was. To do so is to ignore what gives humans value.
B. Secondly, we must deal with future potential as it relates to the concept of preference satisfaction and potential actualization. To best exemplify this, we should look to individuals who DO have moral personhood, but then temporarily lose it. It is unreasonable to put them on the same level as a beings which have not yet even come into existence. The fetus (a non-person) has never had moral personhood nor a self. This means it has had zero preferences. It has no desires; it had no desires. It had no personality; it has no personality. It is and has never been more than a mindless blob of cells. For beings who have had moral personhood, but lost it, the situtation is completely unrelated; the future potential of that being matters because we have stepped into an all new level of potential--post actualization potential. We are, in essense, preventing the future preferences/desires of an already existent, already autonomous person. His wishes continue even if he temporarily is disconnected from the loop. We know that as a person, a man does have an understanding of his existence as a continuing being in past, present, and future. We know he has preferences to keep living.
C. The next item to look at is, "what do you do with individuals who attained moral personhood, but lost it and will never gain it back?" Going by the above system, the conclusion is simple. You have no moral personhood if, given post actualization, you have no chance at reattaining those criteria. If you are a veggie and likely will be so forever or an exceedingly long time (best to appeal to medical prognosis), then you forfeit moral personhood. You simply have not and will never again meet required criteria. THere is no reason for attatching rights and privlidges to such individuals, and given that there is no extrinic reason to keep a perma non-personhood being alive, you ought not be required to do so.
5. Another point to look at is related to the nature of the Fetus. What is a fetus? A fetus is a an organism which grows inside of the mother, is housed there, feeds off of the mother, yet does not contribute anything to the heatlh, vitality, or success of the mother's body. What doe sthis sound like? Medically, a fetus fits the discription of a Parasite. A fetus is a parsite. For quite some time, it cannot even survive on its own, and even after it can, it still feeds off of, is housed in, but contributes nothing to the health of the host. It is disutilitous for a being which has attained moral personhood to be forced to house a parasite within its body against its will. There is no "right" to use someone elses body that comes with moral personhood. Even if we were to assume that a fetus is a moral person, which it isn't, it is still irrelevant, because the right to life does not entail the right to life at any cost. You don't have the right to live by sharing someone's body. Said rationally autonomous host is perfectly justified in cutting you off.
Conclusions: One major conclusion of the above criteria is that being human is not what makes us valuable; what makes us human is valuable. This is independent of species, because it is quite possible that other species exist that have the same qualities, although they are not human. Consequently, these characteristics, to some degree, are also present in various other organisms, although not to the same degree as in humans. However, the logical conclusion of the position is that regardless of species, one should treat two beings with equal consideration given that they have rough or equal parity in terms of personhood or preference satisfaction. If one being does not meet the criteria for moral personhood and never will, or has, but never will again, but the other does or will, then the former actually has less value prima facie than the latter.
IE. A human adult in good health has more value than many other animals, including the Bonobo Chimpanzee. However, the Bonobo has more moral value than a Human vegetable. A Bonobo Chimpanzee has more moral value than a newborn stuck at the mentality of a 1-2 year old. A Bonobo Chimpanzee adult has more moral value than a fetus that will never be born.