There are many issues riding in the developments that could be made in genetic engineering. The manipulation of nature could have unforeseen consequences. Just like introducing a new animal into an ecosystem has an irreversible effect on the environment so could messing with genes introduce a permanent change or side-affect ("Genetic Engineering Advances").
It also becomes a religious issue, "which questions whether man has the right to manipulate the laws and course of nature" ("Genetic Engineering Advances"). Also if it becomes the norm to genetically manipulate human genes, will there be a point at which it is required by law? Regulated by the government?