The risks of abuse far outweigh the benefits when it comes to eugenics and genetic engineering. It can easily be abused by people that want not only to cure diseases but to enhance physical features. 
The research spent on eugenics should be spent on curing the actual diseases themselves. It would be far more beneficial to develop a cure for a specific disease rather than spending millions of dollars on research for eugenics. The possibility of curing disease is only a small portion of eugenics, while the rest is filled with the desire for physical enhancements that are not needed. Wasting valuable time and resources on enhancements rather than diseases is unethical.