Well, incest originally was labeled illegal because inbreeding leads to “very ugly and handicapped children”.
Today there are many cases where the cause for punishment of this “crime” is no longer existant. If a couple consisting of siblings is willing to let themselves sterilized for the sake of continuing their sexual relationship, for instance. If the siblings are female or male twins and homosexually attracted to each other.
In all those cases the danger of creating handicapped offspring is zero, so the cause of it being illegal is no longer existant.
Of course the parents will still be pissed by being deprived of the possibility of having grandchildren (at least if they have not more than 2 children, which would be grand of them because - well, see the overpopulation-thread for this).
But what I really wanted to tell: There are possibilities today that a serious incestuous relationship could be allowed to continue without being labelled illegal, cause there are means to prevent conception during sexual intercourse. And the threat of having abnormal children was all that made it illegal in the first place.
Not wanting to promote incest, though. I know some beautiful twin girls who have thankfully developed to be sexually active, heterosexual individuals with a differing taste in men. It would have been a shame if they had fallen in love with each other instead.
Also, on topic: I’d prefer having a vagina. I would totally take the monthly pain and bleeding for the benefit of having internal private parts - and don’t forget that a pair of breasts comes with the package! Sometimes I really feel sexually inferior to women because I am a man. The only really sensitive erogene zone on my body is my fuckin penis! My girlfriend could have an orgasm without me ever touching her between her legs! That’s fuckin superiority! I DO WANT!