It goes against established legal, ethical and medical understanding. The practice has already been outlawed by the European Convention on Human Rights and Biomedicine, covering not just the EU but all European states. Ethically there is a widespread international understanding that to clone a human being is wrong. To clone is to exercise an unprecedented control over someone else's complete genetic makeup. It is quite different from the randomness of identical twinning, where an embryo of unique and so far unknown genetic type spontaneously divides.
Cloning takes the genetic material of an existing person and uses it as the basis of a new person.
This does not mean an identical person, of course. For the first time a person would come into the world who had had their genes preordained by someone else. We argue that this is intrinsically wrong. We can reject our upbringing, education and social influences, but we cannot change our genes. Equally important, it would be unthinkable in terms of medical risk.