http://faculty.polytechnic.org/gfeldmeth/45.marquis.pdf
There's a few major problems with this though.
1) It does not follow that potential human life is inherently the same as developed human life.
2) It generalizes far too much, when abortion in of itself is a special case.
3) It ignores the rights of the woman in question.
A sperm and ovum joining do not magically, immediately imply a value equal to that of an autonomous being. This new entity is biologically dependent upon the mother's body and cannot be separated. It is not capable of thought, feeling, awareness, or anything. It follows a rote biological path of development utilizing the mother's body as a resource. The most logical thing to do is view it as a part of the mother's body, not a separate entity, as it has no characteristics of a separate entity, and only has the
potential to become a separate entity. Is it not the mother's right to decide what happens inside her body? Are we now suddenly valuing the potential of something more than an actualized human being?
Trying to apply this theory of the right to life because it deprives the subject of all future valuable experiences I have no inherent issue with, though I think it's oversimplified and an unnecessary statement. Life has the right to life, but it is clearly not wrong to kill always. A generalization on such an important statement is unacceptable. Instead, working back from the initial principle and establishing cases where it is wrong to kill makes far more sense. Abortion is one such instance, because we must account for the rights of the woman in question to control her own body. It is wrong to kill, except when it's not. A simple statement which upholds the value of life, except when demonstrated not to. The statement itself holds no power, yet provides a basis for all further reasoning. Many reasons can be provided as to why life has the right to life, yet any pitfalls in those will still come to that inevitable conclusion, because life is inherently a valuable thing.
The third is really a restatement of the first two, but so important and nearly always forgotten in the anti-abortionist's stance. When discussing abortion, we are talking about
two beings at least. It is not intellectually honest to assert that an abortion is murder of an innocent, as if that innocent party was just laying on the ground doing nothing but trying to grow. It's not. It's inside another human being, a human being who might not want it there. A human being who will be permanently affected by having it there, whose body is being used as a resource by this other being to grow. When talking about abortion we have to consider that there is more involved than ending the potential a fetus represents. I hold that the woman has the right to control what happens inside her own body, and that the fetus' inherent right to life does not exceed the woman's right to choose because it is a, incapable of thought, b, has never experienced consciousness, c, cannot survive without its host, and d, is not fully developed.
Abortion is undeniably the ending of a form of life. It is not an immoral form of ending life. I would argue that aborting a fetus that is capable of life outside the mother should constitute as murder, because at that point enough time would have passed that the mother would have made her decision (or should have) on whether to keep it. Likewise, I would consider it murder to cause a pregnant woman to abort unwillingly, regardless of the developmental stage of the fetus, because she has given her consent to the being inside of her and values it and it had the potential to become a fully developed human being. I do not consider it murder if the woman wishes to abort, because the fetus is not yet capable of independent life and thus is a part of her body.
We do not consider the potential of something the same as the fully developed version. We do not prioritize potential over actual. I will not argue that abortion is not ending that potential, because it is, but it is the woman's right to do so.
That is what abortion is about. Not the fetus. The woman. I do not care whether you want to call a potential human a human. That does not change that situation, but is just an argument from semantics designed to distract from the issue of whether the woman has the right to control her own body. You think it's wrong? Swell, don't abort if you get pregnant. But no one has the right to tell another what is going to happen inside their body against their will, period. Is it irresponsible to engage in unprotected sex that may result in a pregnancy? Absolutely. That does not nullify the right to control one's body, and any argument that the woman should keep it as punishment for her mistake is beyond monstrous.