The issue of stem cells being used for medical purposes is mainly a conflict between religious and ethical points of view on the one hand and utilitarian and scientific points of view on the other. The major pro of this use of stem cells is that it could be a way to create new therapies for many diseases. The major con is that stem cells are seen by many people as potential human lives.
On the pro side, stem cell research could be extremely beneficial to many people. This has not been proven yet, but it is very possible that stem cell research could lead to discoveries that might seriously improve human life. Stem cells might be used, for example, to regenerate cells and tissues that are affected by such things as Parkinson ’s disease and Alzheimer’s.
The major con about stem cell research is that it might be tantamount to using human beings for medical testing. Stem cells (embryonic ones, at least) are cells that come to exist soon after a sperm fertilizes an egg. Because of this, many people think that they are a form of human life. Using human life to conduct medical research would be morally abhorrent.
Thus, this debate is largely a debate between those who think that stem cells are potential human beings and those who do not feel that way.