By getting experience in this field of science, we may learn enough about the human genome to correct genetic defect diseases such as Parkinson s, or Alzheimer s. We could also clone the appropriate gene strands to correct other disorders such as infertility. The most important thing we could learn from our genetic experience is the ability to switch cells on or off which may lead to a cure for cancer. Most people feel that human cloning and genetic splicing or hybridization could irreversibly contaminate the human gene pool. People fear that if cloning is allowed the people that are against it may do demonstrations or terrorism to protest human cloning.
Many religious groups are also against human genetic manipulation.
Genetic engineering can be used for many useful purposes. For instance you could make a plant more resistant to a virus or insects by just splicing it with another plant that is resistant to those things. In the environment, genetically altered bacteria can breakdown pollutants and garbage faster. But perhaps more importantly is the medical usage of genetic engineering. Before 1982 we only had a limited supply of insulin for diabetics and it was insulin from a pig.