"Excess" Embryos?

Michael:

If one believes that life begins at conception, does that not imply that the so-called "excess" embryos are living human beings with souls upon whom experimentation would violate the gospel of life? Conversely, if one does not believe that life begins at conception, then why draw a line between creating embryos for the purpose of harvesting stem cells and using "excess" embryos? I realize that this probably won't help sort out the problem, but I am genuinely curious as to why the difference in source matters.

Steve

PS: The Pontifical Academy for Life refers "to the enormous number of human embryos that are lost or destroyed following these [fertility] procedures - a real "slaughter of the innocents" of our times." As I understand it, the harvesting of stem cells from the excess embryos entails the destruction of those embryos, so it does not solvge the problem (in my view).