Glad to see you all again, that this conversation is going moderately well. I need to change the title, too.
The idea behind the first example, while perhaps not clear, was a question of personal freedom vs societal burden. The gene isn't linked to anything, and it causes dangerous allergic reaction to some common substance, such as some kind of mold. We have the medicine to help these people live a healthy life, and natural selection does not occur on a large scale. Sexual selection is barely affected, because "Hey, it's just an allergy". The gene is more likely to spread than it is die out. So now there comes this question of "How can we remove this trait, and does a society have a right to limit personal freedom for the sake of itself? (such as preventing child birth, inability to wed certain people)
Edit: Second example is moot. Looked up some stuff really quick, @eterno was right. No effective way to determine this, so this question has no basis in reality. The second question is suppose to reintroduce feasibility, but isn't feasible.
And finally, I'm glad somebody brought up Eugenics. It's a similar concept, but poorly executed. People were being selected against for non-harmful traits, phenotype, and racial distinctions. The idea was applied to remove social traits, rather than survival traits. While they used sterilization in many cases, the Nazi's also used euthanasia in their Eugenics program. Also, note that the Nazi's aren't the only people who tried to have a Eugenics program. For Americans, check out the Immigration Restriction League.