Protip: Any negative phenotype is very unlikely to be inherited to future generations. Either the subject dies quite early, or is not able to reproduce, or is too socially excluded to find a mating partner.
Therefore, any negative phenotype that can be inherited must also have positive effects.
Edit: Lost my respect for @guardian3.
Edit #2: I suggest changing the thread title. "Ethically" is too close to "ethnically", which is what I read first. You could replace it with "in a morally acceptable manner"
Edit #3: I think I should add an example of a negative phenotype having a positive effect: the sickle-cell anemia shortens your life expectancy, but makes you more resistant to malaria mosquitoes. In a context of an acute threat of malaria mosquitoes, people with the sickle-cell anemia would actually have an advantage.