Many people state that incest must be kept illegal because children bred out of incest tend to be genetically undesirable, afflicted with disorders that will only poison the human race. However, what these individuals forget is that there are many other afflictions out there that do not require an incestuous relationship to spread into offspring. For example, sickle cell disease, heart disease, cololor blindness, and baldness are all inherited from one's parents. A child can even receive HIV from an HIV-positive mother.
Therefore, if we really care about the genetic purity of humanity, we must have the government ensure that only the purest of individuals pass their genes onto the future. By having the government prevent those who carry bad genes as well as those most likely to suffer from a disease (i.e. Japanese and colon cancer) from breeding, we can be sure that our nation has only the purest of people. After all, we've already banned incest because it can lead to tolerable disorders. Therefore, it wouldn't be a violation of civil rights to extend that ban to the rest of the riffraff.