Clones are genetically identical individuals. Cloning can occur naturaly (though rarely) -- for example identical twins are clones. Nowadays, when people talk about cloning, they don't mean naturally occurring twins. They are referring to a technique called somatic cell nuclear transfer ('SCNT'). This is done by transferring the nucleus from an adult body ('soma') cell -- like a skin cell -- into an egg cell which has had its chromosomes removed or inactivated. SCNT produces an embryo that is virtually identical to the adult cell donor.
All human cloning is reproductive. It creates a new, developing human intended to be identical to the cloned subject. Both "reproductive cloning" and "therapeutic cloning" use exactly the same technique to create the clone, and the cloned embryos are indistinguisable. (For more on embryonic stells, you might want to read our article about Stem Cells).
SCNT produces an new, single-cell embryo and grown in the lab for a few days. Then it is either implated in the womb of a surrogate mother ("reproductive cloning") or it is destroyed to harvest the embryonic stem cells for experiments ("therapeutic cloning"). It is the same embryo, used for different purposes. At that stage of development, a cloned embryo looks just like an embryo created by fertilization.
Biologically and genetically speaking, what is created is a human being, a member of the species Homo Sapiens. If this being is nourished and protected, it will proceed uninterrupted through the developmental stages of embryo, fetus, newborn, toddler, child, teen, adult and aged adult: one continuous existence. This being never develops into a pig, a frog or a tree, but only into a human. This being is therefore, by definition, a living human being.
Cloning is very inefficient -- more than 95% of clones die before or soon after birth. Most cloned embryos do not survive for even a week. Experiments with animals show that even these early embryos have abnormalities. Out of 277 cloned embryos, only one sheep, Dolly, was produced. She had so many abornamlities she finally had to be destroyed. The same rate of failure is seen in all mammals that have been cloned. Furthermore, because of the abormalities, the health of the surrogate mother carrying the clone can also be in danger.
Therapeutic cloning is obviously not therapeutic for the embryo -- the new human is specifically created in order to be destroyed as a source of tissue. Theoretically, the embryonic stem cells taken from the cloned human embryo would be used to generate matched tissue for transplant into the patient from whom the embryo was cloned. However, there are no therapies currently available from therapeutic cloning, and none in the foreseeable future.
Moreover, when the technique was used in mice, rather than producing matching tissues, the cloned cells were rejected. Even if we get past the abnormalities caused by the cloning process, embryonic stem cells have a tendency to form tumors, and it is difficult to have the cells form correct tissues and behave normally.
Cloning is very inefficient, and an enormous number of human eggs will be needed to create even a few cloned human embryos. Even the 'best-case scenario' estimates that it will take 50-100 human eggs to produce just one cloned embryo. There are about 17 million diabetics in the U.S., which means that in order to treat them all, you would need at least 850 million to 1.7 billion human eggs. Human eggs come from only one source - human women. You'd need about 85 million of them, just to treat diabetics! And donating eggs does carry health risks from the high hormone doses and the surgery to remove the eggs.
The result, of course, is that eggs would be rare commodity, and the poor and disadvantaged will be exploited.
