Discussing ways to improve the quality of the human gene pool is seen as a dangerous topic because it is one of the basis of Nazi ideology, which means most people simply don't want to have that discussion for fear of how it could be interpreted.

Using natural selection, adaption takes millions of years to happen. Using artificial selection adaption takes thousands of years (think dogs and domestic livestock). Using genetic engineering, adaption can happen in a couple of generations.

The risk here is that, seeing as genetic engineering will initially only be available to the elite, it won't be long before we have a class of 'super people' ruling over the rest of the serfs. It's not hard to see why that idea would make some people uncomfortable.