I'm not sure you want to go there either. The genetic consequences of incest have generally been a myth. It's only when you get generation after generation of inbreeding that you start getting the Haspburg jaw and the like.
And even if you want to rely on the genetic reasons, that would still potentially allow marriages between, say a father and an adult, adopted daughter.
all arguments for gay marriages come crashing down once the issue of public health is introduced.
Unless gay marriage would curb promiscuity.
Which is exactly why such a marriage is permitted by law as far as I know.
Unless gay marriage would curb promiscuity.
Like heterosexual marriage has curbed heterosexual promiscuity? /sarcasm off/
Now that's the kind of argument the gay community really wants to hear -- gay people have so little control over themselves that a legal contract is needed to keep them under control.