3. Genetic EngineeringPerfect humans. Engineered from before birth to be the best of the best. What could be better than having the perfect child, with no possible risk of inherited flaws? All without the use of those messy nanobots. I think the movie Gattaca (1997) says it best:
We want to give your child the best possible start. Believe me, we have enough imperfection built in already. Your child doesn't need any more additional burdens. Keep in mind, this child is still you. Simply, the best, of you. You could conceive naturally a thousand times and never get such a result.
The danger arises not from any physical aspect of genetic engineering, but rather the social aspects. When you begin to breed perfect humans, you create an entirely new social class. Bringing discrimination to new levels, the class you belong to will not be determined by social status, income or the color of your skin, rather, the build of your genes.