lavendersparkle

I think a problem with that argument is that we don't generally think it should be illegal for two people to have sex if they are both carriers of a horrible genetic disease. We don't think that people who have horrible non-recessive genetic diseases should be oblidged to never have potentially procreative sex or be sterilised. You could make an argument that conceiving a child that you knew to be at high risk of having a genetic disease would be immoral. However, I don't think that very rare parenting between close relatives would be that likely to result in children with genetic problems unless the parents had a particular genetic problem to begin with.