"Please tell us how you know whether anything is morally justifiable. Give us your standard."
Morally we should not infringe on the rights of other humans. We should seek to better ourselves and society without infringing on the rights of others. I think we have a moral duty to both ourselves and the objects to not commit acts of cruelty. Thus my answer to earlier questions on animal rights. I think this is a universally agreeable statement. Let me know if you think otherwise.
I provided earlier my positive definition of human, but I will attempt to provide it again in stronger terms.
I do not recognize the "human at conception" definition as defensible. Physically and theologically there is a major problem: a large percentage of fertilized eggs (the earliest stage you would define as human) do not implant in the uterus and are therefore evacuated from the women as part of an apparently normal menstrual cycle. In September 2003, John Opitz, a professor of pediatrics, human genetics, and gynecology at the University of Utah provided the President's Council on Bioethics with the estimate that 60-80% of all fertilized eggs fail to implant. This is why doctors define pregnancy as the implantation of a fertilized egg rather than the conception itself. The medical point of all of this, is that between these unimplanted conceptus and miscarriages, a significant percentage (possibly even a majority) of all fertilized eggs never reach birth. The theological question here is why god would give a conceptus a soul only to recall that soul to heaven within a few days. Even more problematic is that if god does accept all of these souls into heaven, more than half of the souls in heaven never drew breath on earth or even developed fully enough to have a brain and form thought. This definition of human begs too many questions.
There are scriptural reasons for not accepting the "human at conception" definition also. Most notably Exodus 21:22. This passage has been hotly debated for a while, so I'm sure you're familiar with it. In other scriptural arguments, the bible first presents us with humans in the form of Adam and Eve. These are the starting point definition of human as I'm sure you'll agree. The Bible tells us, and most of you have reminded me, that man is created in God's image. And yet this has more meaning than the physical image of God, which has little if any meaning. To say that god actually has hands or feet has often been viewed as a heresy. What then does the image of God refer to. Power over earth and free will. All humans have power and free will, and in the protestant faith, all humans are priests and have direct communication with God in the form of a conscience. A zygote has none of these features. It does not have power, free will, or a consciousness - it does not have a brain. This is why, up until about the time of Darwin, most people accepted the ensoulment of the person at quickening or at birth. Ensoulment made more logical sense if matched with a mind / brain.
In that I do not find the "human at conception" definition acceptable, I have had to formulate a different definition. Luckily, these problems have been recognized since at least Aristotle. One possibility is that ensoulment happens at quickening. This was the long held belief of the church drawn in part from the writings of Aristotle. Augustine and Aquinas both held some version of this definition. While I do not agree with this definition it coincidentally lines up with mine as far as the timeline goes. The traditional idea of quickening is that it happens somewhere around the halfway point in the preganancy cycle. This matches chronologically with my idea of defining a human as a rational / sentient being.
I said this earlier, but it was apparently missed or forgotten:
"My positive definition of human:
I define humans as rational animals / sentient beings. Medically this development of sentience is though to occur around the same time as viability (perhaps even a little later). Something like 26 weeks. Personally I cannot imagine aborting a fetus this late, and prefer the viability date at say 20 weeks or 22 weeks (earlier gives some slight chance). Nonetheless, my philosophical position that I will seek to defend in this forum is that humans are rational, sentient creatures. Once sentience and rationality are achieved, a fetus becomes a human. Until they are irreversibly lost, they remain a living human. By rational and sentient, I include those humans that are asleep or severely mentally handicapped - their brains are still functioning - but am open to a case by case study of people who are brain dead - measuring for permanence and irreversibility. I will not kill a human (unless it is trying to kill me - see below). I am against late term abortion (which is rare - about 1% of all abortions occur after week 24) unless in the case of absolute medical need (which is often the case in such late term abortion since it is so universally reviled otherwise). I think abortions should be available but limited based on the above statement."
You didn't tell me how you know any of those things you merely asserted. Is it your position that everyone is supposed to listen to your moral pronouncements and bow the knee to them? What is your authority, that we should agree with you?
Also, if we shouldn't infringe on the rights of other humans, how does that allow for our preemptively defining them out of existence? The slaveowner can do that with his Negro slave. You do that with very young humans. I do that with people whose initials are "JS". Pretty easy, right? Now you don't have any rights, and I can legitimately kill you if you inconvenience me.
--"Physically and theologically there is a major problem: a large percentage of fertilized eggs (the earliest stage you would define as human) do not implant in the uterus and are therefore evacuated from the women as part of an apparently normal menstrual cycle."
I hate to break it to you, but a large percentage of born humans don't make it to age 80. Tell you what - I can set up an arbitrary cut-off age too. If you don't make it to 80, I'm justified in putting everyone to death who didn't make it to 80. Is that OK? If not, why not?
--"This is why doctors define pregnancy as the implantation of a fertilized egg rather than the conception itself."
1) SOME doctors.
2) Nazi doctors didn't think Jews were human.
3) Slaveowners who were also doctors didn't always think their Negros were human.
--"The theological question here is why god would give a conceptus a soul only to recall that soul to heaven within a few days."
Yes, that is a theological question, and the answer is that God has the right to do what He pleases with His creation. You would too, if you had a creation. But, you don't, so you have to abide by rules, and among the rules God set up are that you don't get to murder humans, not even when they're really really young.
--"This definition of human begs too many questions."
You mean RAISES too many? Just b/c you don't understand them b/c you haven't studied doesn't mean there aren't answers, and just b/c you don't know the answers doesn't give us any reason to think you have a justification for your desire to allow the murder of babies.
--"What then does the image of God refer to. Power over earth and free will."
I don't grant that at all. It means volition, intelligence, and a spirit.
If you disagree, please provide biblical exegesis to support your argument.
Besides, 2-year olds don't have "power over earth".
And you have no idea whether 1-week-old fetuses have free will. You ASSUME they don't, but you can't prove it. It's more convenient for you to assume the nonexistence. Again, you're revealing you have no certainty. You're just guessing. You're firing into the rustling bushes 500 yds away.
--"One possibility is that ensoulment happens at quickening. "
Which is not a scientific category.
And which happens at a diff time for everyone. It's just arbitrary. Besides, it's easy to redefine "quickening" to suit one's own desires.
--"I define humans as rational animals / sentient beings."
1) 2 year olds are hardly rational. I guess we can kill them.
2) If I'm a slaveowner, I just remind you that Negros aren't rational. They're really dumb. And they're barely sentient. See? Problem solved.
3) You don't know whether fetuses are rational or sentient. You assume they're not. Where's the argument? A naked appeal to "brainwaves"? For one thing, brainwaves appear a long time before you're willing to say it's not OK to kill the fetus. For another thing, you don't know for sure that brainwaves=cognition. You assume it.
--" my philosophical position that I will seek to defend in this forum"
So far you've given us little more than naked assertions, as if you're some sort of authority. When are you going to start DEFENDING your position?
--"By rational and sentient, I include those humans that are asleep or severely mentally handicapped - their brains are still functioning"
Well, I exclude them. Their brains are clearly NOT functioning, not like mine. And that's the rub, isn't it? They don't function LIKE YOURS. Who's to say I'm wrong in insisting we can legitimately kill retarded people?