Michael S. says:
If we as a society hold human life sacred (even in some secular sense), we can’t discriminate between types or stages of human life. We cannot conclude that some types human organisms have more worth than other types or that human organisms at some stages of development have more worth than those at other stages.
This brings to mind a hypothetical that I've seen float around lefty blogs a bit as a means of challenging just this claim, and I'm curious how you all would respond. When I've seen it in the past, I've often thought it's a bit silly, but it does seem relevant to this discussion. Here it is: you are outside a burning building, and, inside the building are two bedrooms. In one bedroom are 2 six-month-old infants. In another room are 2 blastocysts in a petri dish. You have time to make one trip into the house before it comes crashing down. Do you grab the blastocysts or the six-month-old infants?
I assume that everyone would grab the infants (the point of the hypothetical). Is this a prohibited form of discrimination between stages of life or is there some other justification for favoring the infants that does not violate your principle of equal regard between life stages? Note, I don't think favoring the infants here results in the conclusion that stem cell research is permissible; there is obviously a difference between chosing whom to save and actually intending to cause harm to something or someone. But I do think it goes a bit far to say that one cannot reasonably distinguish among life stages, favoring some over others, at least within certain limits.
Michael then goes on to ask:
How does one who supports abortion or embryonic stem cell research maintain that unborn human organisms and only unborn human organisms are not entitled to the respect and dignity afforded all other human organisms?
Two points about this. One, I am not aware of an argument (even by people who support stem cell research and abortion) that unborn human beings are not entitled to any respect or dignity at all. Nor do I think that the belief that it is reasonable to distinguish between stages of development necessitates support for stem cell research or abortion (see above). Two, I am willing to offer a set of possibilities with the caveat that I am not endorsing them. These are more by way of a brainstorm, although I find some of them to be at least plausible (especially the first three). With that clarification, I can think of several possible normative distinctions that would point towards a different line than conception as the significant one for entitlement to treatment as a human being:
(1) greater than 50% likelihood of developing, in the normal course of events, into a mature human being (which, depending on the science, arguably point towards a line drawn between pre-implantation and post-implantation embryos);
(2)individual (presumably genetic) identity (some have used this to draw a
line distinguishing embryos before and after the possibility of
twinning or -- and I'm not sure what they call this, though it does
occur on rare occasions -- the combination of two separate embryos into
one new embryo);
(3) possession of physical structures necessary for conciousness or the
ability to feel pain; etc. (which would seem to point towards a
somewhat later stage in development, in which the nervous system is
more developed);
(4) possession of a bodily structure recognizeable as human; or
(5) viability outside of the mother's womb.
There are probably several others. These are just the ones that occurred to me off the top of my head.