While many Americans continue to try to halt embryonic stem cell research, Iranian scientists are forging ahead with this cell research with the aim of curing people suffering from real life medical conditions, especially military veterans who have suffered disabling spinal cord injuries. That is the issue brought front and center by this episode of Frontline. In the Shiite view, the soul enters the embryo only once it is viable--only after viability is can the organism growing in utero be considered a "human being."
In the U.S., many of us continue to treat stem cells as though they are harvested from organisms that are fully human, even though these embryos lack the biological equipment necessary for any semblance of sentience. As best I can understand the dispute, many of those in the U.S. who oppose embryonic stem cell research consider an embryo to be fully human even though it has merely the potential to someday become a thinking human being. They focus on the potential rather than sentience--on what will someday be rather than what is.
The Iranians, in focusing on viability, illustrate that two versions of religious practices (conservative Muslims and conservative Christians) that both believe in supernatural "souls" and are both conservative look at the exact same thing (embryos) and come to opposite conclusions.