Thrawn,
Whatever else is said in rebuttal, I think we can all agree that a fetus is not quite the same as a piece of skin tissue or bone marrow.  The fetus develops into a human being, given the opportunity.  The same cannot be said for the other types of tissue.  If they can extract stem-cells from my own bone marrow and use it to cure a disease I have no objections.  But human life is sacred, whether we believe in God or not.  By the time most women know they are pregnant, the fetus has a beating heart and a brain wave.  It is repugnant to me to have something like that killed and then use it's tissue for research, no matter what the reason.
Regards, Shuckins