Someday, if therapeutic cloning goes well, scientists would take a few cells from a person with a disease, say diabetes, and use them to make an embryo that would have the same genes as the sick person. Implanting that embryo in a woman might enable it to grow into a baby who is a clone of the sick person.
Instead, the embryo would grow in the laboratory for about five days to the blastocyst stage, the point at which the embryo has two distinct cell types. It consists of a hollow ball with another ball of cells inside, known as embryonic stem cells. They, in theory, could develop into any of the body's specialized cells. The other embryo cells would be discarded.
In the case of a diabetic, scientists would prod the stem cells with an as-yet-undefined cocktail of chemicals so they would grow into islet cells of the pancreas. That could replace those lost to the disease. Voilà, a cure.
Ok, so millions of human ova (eggs) would be extracted, grown into developing babies, and then harvested for their organs. So how is this more acceptable than reproductive cloning? I have yet to see a coherent explanation.