What are the possible negatives/disadvantages of Eugenic control of the population?
I would say that the main negative with regard to eugenics is that it sets up certain people as arbiters of who gets to reproduce and who does not. Past attempts at eugenics have tended to lead to abuses of human rights.
We can see an example of this from the history of the United States. In the early 1900s, there was a eugenics movement in this country. The movement sought, among other things, the forced sterilization of people deemed to be mentally subnormal. This was not done on a very widespread basis, but the movement did result in many people being sterilized against their wills. By doing this, the governments in these areas of the US were depriving people of a basic human right.
Eugenic control inevitably involves someone deciding who may and who may not reproduce -- whose genes are worthy of being passed on and whose are not. This is totalitarianism of the worst sort.
Eugenics is a practice that aims to improve the human race by selection of parents based on their inherited characteristics. Supporters of this practice suggest that only the persons who are above average mentally and physically should have preference over others in producing children.
The biggest limitation of such practice is in determining with certainty, which traits in human beings are definitely better than the ones opposite to those.Who will be responsible for selecting such persons. Can we be sure that their decision be always correct. It has been observed that the greatest people down the history including spiritual leaders, scientists, philosophers and artists were not appreciated or valued by the established leaders of the society. It is possible that such opposition in society to deviation from the normal will prevent, or at least severely restrict birth of people with highly valuable revolutionary new thinking and ideas.
Also where do we draw the line between the good and the bad. Should the ones chosen as fit to produce future generations of humans constitute 50 percent, 5 percent, or just 0.01 percent of the world population.
Then, it is possible that the future improved humanity through the practice of eugenics may raise its standards of what type of humans are fit to be born and live and what type are not. Or are we thinking of a human race in which all the people are exactly identical to all others. Whenever there is variety, it is always possible to consider some as inferior or superior to others. But is this a reason enough to kill the variety?
The most direct and immediate fall out of practice of eugenics is perhaps the discounting of the values of human equality and basic value of life o all humans. We cannot practice without practically accepting the belief that some type of people just don't deserve to be born. This will give rise to the wrong kind beliefs among people that divides people in classes of fit to be born and not fit to be born.
Then, eugenics also deprives individuals the right of have family. This right is not just the right to procreate, but also the right to love and to be loved by your children. In this way the practice of eugenics can lead to direct undermines the social system of families and that of love and caring we associate with families.