If humans could design their own baby, nothing would stop them from getting carried away. Scientists recently discovered a so-called IQ gene that exists in the brain and that they were able to manipulate in mice. The mice grew smarter, and, of course, interest in whether such techniques could be used in humans raged through the media. Humans could very easily abuse the possibilities of genetic engineering. If people start trying to meet a certain standard, such as blond hair, blue eyes, 5'10'', muscular and intelligent, humans would lose their humanity, and simply become part of a monotone society.
Evolution is a very slow and tedious process that nature has used for billions of years.
Creatures that aren't doing their job the most efficiently get cut from the team and only the elite survive. Within the past few decades, humans have begun to discover the secrets of nature's ways. Humans are beginning to try to outdo nature itself. Human bodies may simply not be ready for a rapid change through genetic engineering. Moreover, if scientists are mistaken in predicting how genetic alterations will affect humans, catastrophic epidemics could arise.