what are the advantages and the disadvantages of stem cells
The reality of the situation is that sacrificing a blastula kills fewer human cells than scratching your nose. The advantages of stem cell research are that they can potentially cure every disease known to man. Each cell in the body (with the exception of red blood cells) carries a complete copy of the individual's DNA.
The disadvantages come entirely from the source of stem cells. For embryonic stem cells, a human blastula (the collection of cells that will eventually become a fetus) must be sacrificed. This brings forth an image of sacrificing babies for science, and needless to say, many folks have a problem with that.