I It is what the US was based off of.
So you're saying humans don't breed humans? Every human goes through a "non-human" embryonic stage on the way to being born?
Yes. I realized after the post that I was using terms rather ambiguously and without clear definitions. In this post, I will use the word "human" to refer to a being which must be respected in order to be acting ethically. Only a human can be murdered, all other forms of life are only killed. I will use "homo sapien" to refer to something that is biologically human, rather than ethically human.
All currently known humans are homo sapiens, but that is not something inherent to the definition. It is incidental to the idea of human. In a similar manner, all hunters wear orange, but wearing orange is not something that is inherent to the act of being a hunter. Being a homo sapien is not a condition necessary to be a human, but is simply a property held by all known humans.
Moreover, everyone understands that abortion kills a developing human. Arguing over whether a zygote, embryo, or fetus is a "person" is pointless because the result is the same. The growing thing/person is killed and will never be born.
I would say that abortion kills a developing homo sapien. The growing homo sapien is killed, and will never develop further. However, I would say that the question of whether the homo sapien is indeed human is of key importance. If the homo sapien is not human, then murder is not possibile. I would not call the destruction of bacteria by my immune system murder, even though they are alive and that I am indeed killing them. Similarly, if the developing homo sapien is not human, then any killing of it cannot be murder. Note that I do not say that if it is human, then the killing is a murder. The condition of humanity is a necessary condition for murder, not a sufficient condition.
Personally, I think if any circumstance can legitimate gives you power to decide life and death, it's when you're growing that life inside you, but people need to be honest about what exactly is going on in an abortion and understand that normal rules for other situations may not apply.
This sounds rather similar to the Unconscious Violinist argument. Even if the developing homo sapien is human, its killing is not necessarily murder. I think that we are in agreement about this, if I have read your argument correctly.
Always draw your curves, then plot your reading.