Cloning as a technology is considered a bad idea at its current level of development because it raises a number of ethical and biological concerns. These include the non-viability of many cloned fetuses, the development of physiological disorders later in life, the increased susceptibility to communicable diseases and other circumstances.
Clones occur naturally in all areas of nature. Any identical twin, human or otherwise, is a clone. Many species of microbes and some species of animal and plants reproduce through cloning. The problems arise from human attempts at creating artificial clones, particularly those of mammals, as the technology is still in its infancy and many factors are unknown.
Well over 95 percent of fertilized clone embryos become non-viable and unable to survive past the initial stages because of genetic defects. Clones that do survive often develop a number of complications later in life, such as abnormally enlarged organs, compromised immune systems and other genetic defects. These factors are troubling ethical dilemmas when applied to the possibility of human clones, as cloning leads to the possibility of human death and suffering.
Experts speculate that clones produced in large number may also all share the same vulnerability to communicable diseases and could be wiped out by a single pathogen. A population with more diverse genetics would prove more resistant. Large populations of clones may also eventually suffer from inbreeding issues.