Therapeutic cloning is a huge 'hot button' political issue and as a result both sides of the debate have muddied the scientific waters in the public's understanding. Before one can form an opinion on the ethics of therapeutic cloning, one needs to know the facts of the science.
The term 'clone' in biology refers to an identical genetic copy of an original. Biologically speaking, identical twins are clones of each other. Bacteria that reproduce by cell division are likewise clones of each other. The idea behind therapeutic cloning is the creation of a stem cell that is genetically identical to a patient and culturing that cell into tissues to cure diseases from congestive heart failure through to paralysis. This stem cell doesn't come from an embryo, but from the genes of the patient himself.
Stem cells come in two basic types - true stem cells and specialized stem cells. While a true stem cell may become any type of cell in the body, a specialized stem cell can only become one type of cell. Cells in the bone marrow may become red blood cells or white blood cells, but they cannot become heart tissue no matter how much we squeeze them. In order to generate the cells that are of most interest to us, we need undiversified true stem cells - the kind that are only present in our bodies in the very earliest stages of fetal development.
When a couple conceives through in vitro fertilization, many embryos are made; this is because the chance of success with any one is very small. On average there are eight embryos left over from every successful in vitro baby. While we call them embryos they are only small cultures of stem cells at this point. They haven't yet began to grow independent tissues. That said, each one does have the potential to gestate into a full human being and thereinwhich is the controversy of embryonic stem cell research. Even though the hundreds of thousands of surplus embryos in the country in any given year become stale and must be thrown away, so sacred is conception to so many people that very little research on embryonic stem cells is being performed.
Therapeutic cloning is an alternative method for generating embryonic stem cells that doesn't require the use of a surplus embryo which could otherwise be adopted out and grown into a living breathing human. Therapeutic cloning, however, has come under attack and this is most likely due to a misunderstanding. Arguments have been made that 'therapeutic clones' will be grown and used as organ donors for healthy people. This cannot be further from the truth as therapeutic cloning doesn't involve the creation of a body; the scientific community of the civilized world would never stand for such a practice. Therapeutic cloning actually just involves an *unfertilized* egg and the DNA from the patient. These raw materials are grown into whatever tissues are needed, but only to fill in gaps within the body, not to create a new body.
The patient's DNA is placed inside the unfertilized egg and we 'trick' the egg into thinking that it is an embryo. It begins dividing to form a blastula - a collection of stem cells. Now it is true that it may be possible to implant this ball of cells into a uterus and grow a cloned human (much as we have already cloned sheep, dogs, cats, and cattle) but the application of therapeutic cloning doesn't ever render this ball of cells into a fetus. Instead the cells are cultured into a line of stem cells which can then be injected back into the patient's own body. Since the cells harbor the patient's own DNA the body recognizes them as 'self' and incorporates them into its structure.
It is hoped that with this technique of growing cells from a patient's own body which mimic embryonic stem cells that we'll be able to cure a severed spinal cord and the resulting paralysis as easily as penicillin brought an end to the horror and death of bacterial infection - as easily as injectable insulin put an end to the horrors of blindness and amputation associated with diabetes. Scientists have been working on rebuilding damaged hearts, kidneys, livers, and other tissues with stem cells; there is even research going on to use therapeutic cloning to make the body resistant to cancer.
Of course there is still controversy over therapeutic cloning even when all the facts are known and understood. No matter how much we uncover in the world of science, it will never be perfectly harmonious with religion and scientists must always be mindful of the will and sensitivities of those who believe in a higher power and the interpretations of their leaders.