bazzer: So, you believe in equal rights for incestuous couples, polygamists, etc? It's a serious question, if they do not deserve the right to marry, why not? I understand these practices are currently illegal, but isn't that, liek homosexuality once was, simply due to social convention? What's wrong with having two wives?
The problem with incest is it leads to a greater risk of genetic abnormalities in the offspring.
This is used to great effect in selective breeding but then you kill any offspring without the desired traits. Hardly something acceptable in human breeding!