That matter that was blown off from a supernova is totally uniform and disorganized. A total "democracy" of atoms I might say. However, a zygote is something else entirely. It has specific parts that make the essence of what it is, and if these parts are removed or changed, the object is no longer the same thing. This is will be my definition of "life".
My supernova comment was in reference to the claim that since all humans were at one point zygotes that zygotes were life.
I'm afraid I don't understand your concept of life either. Almost everything is made up of parts that if you change them won't be what they were. Take a hydrogen atom from a molecule of water and it is no longer water. Take the toxic gas Carbon Monoxide, add an oxygen atom and you'll just get Carbon Dioxide, which is used for carbonation.
If you cut the head off of a human, it is no longer a human in the same sense of what it used to be because the vital organs (brain) make up the essence of a human being such that it will change if they are taken away or moved or changed. But if you cut any part off of a rock, or you remove a bunch of matter from stuff blown off from a supernova, you still have a rock and some matter blown off from a supernova.
True in the large sense. However, I could cut off a hand from my body. Am I no longer a human, because I only have one hand? What if I get an artificial heart? I no longer have a heart but I'm still capable of moving around.
The specific structure of a zygote, who's properties can be altered without any chemical changes, qualifies it as life, and therefore, a human zygote is human life.
I'm not sure what you mean by "can be altered without any chemical change". Could you clarify?
The core of my argument is that a zygote qualifies as life because it's existence is entirely dependent on whether or not certain structures remain intact. This is completely unlike any form of inanimate matter such as a rock or a bunch of matter, because those can exist regardless.
It's two gametes that fused together to make a new cell. I can destroy skin cells, which are human. Is this a human life?
To differentiate this from simple lone egg or sperm cells, an embryo has a guaranteed future. It will grow into a human (regardless of whether or not it actually survives, it will grow) unlike a sperm cell which may or may not depending on circumstance.
It will, yes. But it's not unique in that function. Is a seed a tree? If I go into someone's yard and cut down their tree I can be fined for destruction of property. If I go into their yard and crush a seed should I still be fined the same?
Furthermore, one has to ask whether stopping a life from forming is the same as murder. If I somehow acquired a time machine, and I traveled back 25 years or so into the past and stopped my parents from ever meeting eachother, I have committed suicide because I have prevented my own existence. If I were to die, I would no longer exist as a human because the "democracy" of atoms would be re-established. A dead human is a dead human whether or not it has a head, but a live human no longer exists. By this logic, the definition of suicide would be stopping one's own existence in some method (This could include simply holding a gun to my head or using a time machine. It doesn't really matter). And so preventing a future that is guaranteed, just as an human embryo is guaranteed to grow into a human, is the same thing as destroying it, or perhaps murdering it.
Well I'm going to have to cut your time machine parallel out because it's not scientifically possible (if you could go back in time, you couldn't change anything, since whatever occurred in that time must have already occurred in your time). But if we can accept it philosophically, then this raises a new question. If someone kills someone, are you also killing all of their descendants and children? If I killed someone before he could have a family, and say if I didn't kill him he'd have a bunch of kids, am I still a mass murderer for killing one person? If stopping something from becoming alive is murder then wouldn't using a condom be murder because it stops fertilization?
Now you did specify "to stop a future that is guaranteed". Thing is, about 25% of pregnancies are miscarried by the sixth week, when instead of a zygote it's an embryo.
edit: to Arcpoint - like I said above, the supernova argument was against his argument. Reductio ad absurdum.
At the same point, pictures obviously trigger emotions, but whether it looks like a human or not doesn't really matter. I could make a marzipan baby that looks just like a human, or I could get a dead body and probably morph the remains of it to look like a baby. My own view on Abortion is that it should be legal until the fetus is capable of surviving outside the mother's body. If it can survive outside the mother's body then the only time I'd be "in favor" of abortion would be if giving birth to this baby would result in the Mother's death, though to be fully honest I don't even know if it's possible for a baby to be capable of living outside the mother's body and still have a health effect on the mother.
And I'd define being capable of surviving outside the womb to be past the minimum possible date, and instead to the "likely" area. A fetus with fully developed (or well enough along on development) systems that can survive without much medical care required is what I'd consider the breaking point, not including genetic defects or diseases that makes certain babies require medical care, even past the nine month period.