Advanced Cell Technology of Worcestor, Mass. has developed a method for cultivating embryonic stem cells using a procedure already done for in vitro embryos, which preserves the embryo. A single-cell biopsy is routinely done on embryos resulting from in vitro fertilization when they are at least 8 cells old, to test their viability. ACT has found a way to get the single cell to reproduce into more cells, leaving the original embryo intact. That word "original" is the sticking point.
Advocates of embryonic stem cell research had hoped that this new procedure would satisfy opponents because no embryos are destroyed, but opponents say that this argument is just semantics and "smoke and mirrors". The single cell taken in the biopsy can still develop into another embryo, they say, so THAT embryo is being destroyed for research, and any cell taken from a cluster developed from a single cell is also a potential human being to be destroyed for research. (They object to the biopsy procedure as well, without the stem cell issue, for the same reason.)
Opponents' arguments are mainly based on concepts of murder and killing human beings, but I think there is also the challenge to the concept of "human" that scares the bejesus out of them. Humans can now reproduce without sex, by taking cuttings from other humans, as if they were plants. Until this Brave New World of cell technology, people knew how to define themselves as human beings and members of society, but now the definitions are breaking down, and they feel lost and afraid of losing themselves and their identities. It is the same fear people have of Alzheimer's, or identity theft. Losing one's identity and definition is like a form of death, of losing everything one has struggled to gain, making the struggle seem meaningless, and one's life meaningless as well. Which I think is mistaken.
The discoveries from stem cell research don't make human life meaningless, they make it more meaningFUL. If one cell destroyed means that several lives are saved, it gives meaning to the existence of that cell, which probably would not have had the chance to exist if it weren't for that purpose.
As for the identity and definiton issue, the person you become based on what you've known and done is still the same person, no matter what you find out about your past or shape of the universe. You're still you. People are still people. The only thing that changes is what you do with the information, and whether you make yourself better or bitter with it. How you define yourself is only meaningless if you make it so, and the same with defining human beings. Changing the concept of "human" doesn't eliminate it or invalidate it; it gives mankind the opportunity to give the concept even more meaning and definition. It's wasting the opportunity or rejecting it that would make us meaningless, and just mean.