Stem cell research could save the lives of people with genetic or degenerative disorders. Harvesting stem cells from embryos could destroy the lives of the embryos. The ultimate ethical dilemma here is: is it right to kill one person so that another can live?
First of all, we need to decide whether we should consider an embryo a person. Pro-life groups would have no doubt at all. A person's a person, no matter how small -- even if they're only one cell big. Of course, this doesn't mean that the millions of dead skin cells we shed every day are people. It is the potential the embryo has to develop into a person that makes it human.
But it is precisely this potential that makes a stem cell so useful in research. For an embryo to develop into, eventually, an adult human, its cells must be capable of turning into every sort of cell in the body. Hence the possibility of their use in the sort of disease that involves irreparable damage to irreplaceable cells.
The researchers will say that an embryo is not a person. How can it be? It's a clump of undifferentiated cells. It can't think, it can't feel, it bears no resemblance to a human being. At some point during development it becomes a person, but just because the line is broad or fuzzy doesn't mean it isn't there.
Moreover, some of the cells most useful to research will be those that carry a genetic disorder -- taken from embryos discarded during IVF by parents who were looking for a healthy child. These would normally have been destroyed anyway. And of course this raises the question of whether this is morally right, too. Should we pick and choose our children in this way? Do we have the right to kill off people that we think wouldn't have much of a life? Does it count if we do it before they become people, or is future personhood important too -- should we take account of "what would have happened"?
It's worth investigating the possibility that embryonic stem cells can be harvested without killing the embryo. One cell can be removed from a group of eight or sixteen, leaving the others behind to continue to develop. The trouble is that embryos are so small and fragile that a lot of the time even this kills them. And how can we further develop a technology for live harvesting without doing some tests that are going to kill some embryos along the way? And is this a price worth paying?
So no, I don't have any answers, only questions. But in a way I'd be frightened of anyone who did know the answers. If it were a matter of people voluntarily giving their lives, it would be easy. They would be heroes, sacrificing themselves that others might live. We would admire them, and then pass laws against it, just in case anyone felt under pressure. Because to hold that power over someone, something, else, is an awesome responsibility.