Synthesis of drugs
This allows to synthesize chemicals which can be synthesized not or only with high costs in a conventional fashion, so it may make some sense. It is important, however that conventional methods have been tried first. Furthermore, a 'null emmission' should be the main goal. The current laws do not demand this.
Genetical screening
Imagine this, you are looking for a job and you don't get one because you will die in ten years from a genetical disease. Gene screening is very tempting for employers and insurances and will lead to a new kind of 'glass human'. It is very important to prevent these guys, to select their employees with this method. Instead of making dangerous working spaces safe, the best worker for an unsafe work will be chosen. This is definitely wrong and inhumane.
Somatic gene therapy
This involves an extraction and manipulation of human body cells. These cells can be implanted in a sick body, where they can perform tasks, for example the synthesis of chemicals which can't be created by the patient's body. Somatic gene therapy may be used to heal some rare genetical diseases like some rare forms of leukemia. Again, somatic gene therapy should be used only when everything else fails, especially because it involves a release. If you ask me if I would prefer to die or to use somatic gene therapy, then I would answer: I want to live, of course (My deepest apologies to all fanatics). But the diseases which can be cured with somatic gene therapy are rare and far between, so I see no reason to worry about it. Furthermore, this type of manipulation shouldn't affect the children of the patient.
Germ-cell gene therapy
The same doesn't hold for the germ-cell gene therapy which is the most sinister application of gene technology in the medicine. Here are the germ-cells manipulated and the organism which will hatch from these cells bear the manipulation within them. They will give the new genes to their children and the children of their children, so the manipulation is PERMANENT. This leads to a form of breeding 'new' organisms. With plants and animals, this is already performed (unfortunately), germ-cell gene therapy on humans is not allowed yet (fortunately). I guess that, since germ-cell gene therapy cures only diseases of people who are not born yet, it is absolutely unnecessary and should remain a dream of mad dictators and eugenic scientists forever.