Gregg at Pundit Review knocks it out of the park with his response to these comments by Roger Pilon in WSJ
Whether we believe that the right to life begins at conception or at some point over the next 270 days, we all believe, I hope, that it begins at some point along that line. We all agree, there is some point at which abortion amounts to murder we just cant agree on where that point is.
Gregg fires back:
This is utter nonsense. We should be able to agree on when life begins since it is an undisputed empirical biological fact that can be found in any first year medical students embryology textbook that life begins at conception when the human sperm fertilizes the egg-called the process of fecundation. Any other arbitrary demarcation of when human life begins contradicts this scientific fact. There is no debate on when human life begins.
Read the rest at Marlowe's Shade
I'm having trouble seeing how the second statement counts as anything close to a response to the first statement. The first says that it's unclear when a right to life begins. The second calls such a view nonsense but then supports that conclusion only by saying that we know when life begins. But knowing when life begins doesn't give us enough information about when a right to life begins, not without a further philosophical (and not medical) claim. That further claim is that a right to life begins when life begins. But that's the very issue that's in dispute between most pro-life and most pro-choice people. Simply assuming it is not fair game in a philosophical argument. I happen to agree that the right to life begins when life begins, but you can't hope to think people will look at your argument as worth paying attention to if you slip between these two things without acknowledging that whether these two go together is the controversy.
Maybe the use of language could have been more precise. Gregg is equating human life with, to use current bio-ethical term, "personhood". I wholeheartedly agree with him that when you have fertilized embryo with a full set of genes contributed by both parents, you have human life and that child has a right to live from the moment it is conceived, not at some point during gestation, or even in the views of bioethicists like Peter Singer or doctors in Holland, at some vague point after birth. I think that except for those who over-emphasis the intellectual, this is a self-evident truth. And questioning this inherent value of life plays right into the hands of the Culture of Death.
Why throw out a logical and intuitive reason for an abstract "philosophical" one? Singer is considered by many as one of the greatest living philosophers because of his ability to construct rhetorically appealing utilitarian arguments for abominations such as infanticide and bestiality. To those with a relativistic moral worldview, these arguments are irresistible. Only those of us who "philosophically assume" there is an absolute moral standard that we are held to can oppose this materialistic logic.
That isn't to say that we shouldn't develop equally compelling reasons that would appeal to those who don't share our assumptions, I believe that sound parallel arguments are always there. But in this case I think Gregg's gut response is reliable. Is there anything useful for us in separating the right to life with life itself?
I don't think there's any question that once an egg is fertilized, life has begun. And that life is the beginning of a human being. The question is this - Does that 2-celled life form have human rights that supercede anything the mother might want to do to harm it?
If you look at it from a Christian point of view, then the answer is obviously yes. But if you're trying to convince people who aren't Christians to agree with you, then arguing on Christian principles isn't going to get you anywhere.
So here's the problem. By the time a woman knows she's pregnant, she has a very small fetus with no appreciable brain. The fetus is also likely to be much less intelligent and self-aware than many animals.
So you either need to argue that all life of any form is valuable, which opens up a whole can of worms about how animals are treated. Or you need to argue that a fetus which is still likely to be non-sentient is worthy of having its own right to life, even if that contrasts with the mother's wishes.
It's a tough argument. But it's either that or convert everyone to the same religious views, which I think is even tougher.