Scientists should be responsible for their researches.
It is quite a difference whether a scientist does research on an automobile or whether he does it with living creatures. On the one hand research is important. For instance, in the research of new remedies. If there had not been any research in this field, we would have had to fight against diseases from the past. But when I think about genetic engineering, I ask myself whether it is morally justified. It might be an advantage, to prevent serious hereditary diseases through genetic operations or from suspected abnormalities. However, it is not acceptable to put any human beings through such operations.
On the other hand the thought of creating people, whose gender or skin colour, might be influenced or to create people who have three lungs, three kidneys or two hearts, just to be able to donate an organ without losing their own quality of life, is certainly interesting.
(This list of nightmare scenarios could be continued with making people who are high intelligent or especially stupid, just to have people who would achieve higher or lower activities, human fighting machines and so on.)
Even so, it should be very clear for every scientist that this is a capital change in the nature, which is not right at all and of which he has to take the responsibility.
In my opinion, a scientist should only do research which is acceptable for humanity. Unfortunately the former results of history have often shown us the opposite.