Blind Guardian
Member
Mental disabilities are not always passed on to offspring. Though severe mental retardation is fairly likely to be passed on, genetic predisposition in offspring isn't the case with milder cases of retardation in parents. Remember, too, that parents of average or high intelligence stand a chance to have a child who suffers from retardation. These are among the reasons why the United States and other developed nations do not practice eugenics and sterilize any longer.
Still feels like the chances for an incest baby to be born with defects isn't any bigger than a kid with two disabled parents.