Research into cloning began at the turn of the twentieth century, though major developments hadn't occurred until modern times. Human cloning, in particular, is debated across the world and has stirred up major controversy. The disadvantages, which are ethical, biological and theoretically social, appear to many to far outweigh the advantages of cloning.
The process of cloning humans is likely to create physical abnormalities in the cloned foetus. If cloned from adult cells, the rapid ageing of these cells can cause these abnormalities and force scientists to destroy the faulty clones.
From a social standpoint, clones are likely not to be accepted into society quickly or easily. A major disadvantage are the unsettled questions relating to the lack of rights of the clone and the idea of ownership of a clone.
The disadvantages of cloning are important to look into because they are likely to cause great social and moral upheaval in society, should cloning become allowed.
Theoretically, cloning could open a new lesser class of human beings. Intolerance has long been present in history, and it is likely that human clones will face just that from non-cloned humans in many parts of the world.
It is important to consider that most of the disadvantages to cloning are completely theoretical, though history has shown the way people react to things they don't understand and things they were against in the first place. Since most Americans, for example, are against cloning, clones are not likely to be received well in the United States.