Eugenics is morally unacceptable because in application it is abhorrent and logically flawed.
There are so many “normal” people who are selfish, vicious, abusive or ignorant by choice.
So many “normal” people could be deemed “a waste of skin” for some valid reason.
As others have pointed out, there are congenitally imperfect people who have and are and will continue to make valuable contributions to society.
There is no way to known in advance who will accomplish something that will make the life of someone better.
We get to judge people (in our courts) on the basis of their behaviour.
We get to evaluate a person’s contributions after the fact and then we can predict their future potential ex post facto.
No person can evaluate the potential quality of an other person’s life to them. It is an internal, uniquely personal assessment.
Economic value versus cost to society is not a criteria we apply or are willing to apply.
If we were willing to do so, convicts sentenced to terms that would exceed their life expectancy would be routinely executed to save money, without regard to their crime or any other attribute.
By our inaction, we allows untold numbers of people to die of preventable diseases, hunger and thirst. We treat many pets better than we treat most people at risk.
We already practice Eugenics by choosing not to assist people whose countries have no economic or strategic importance to countries rich enough to save their lives, while the same countries spend uncountable trillions of borrowed dollars to wage war and develop more powerful awful weapons of human annihilation.
We have access to inexpensive drugs that would cure or prevent diseases. The drug companies don’t make them because there is not profit in it because copyrights have expired. We don’t demand and send out these supplies because powerful countries see not benefit to them. The sick and at risk have “undesirable racial characteristics” and do not possess or produce commodities we want, therefore these people have no value!
We can’t stomach active Eugenics but we practice passive, inactive eugenics every day!