I have to admit that I don't really see anything morally wrong with incest, as long as it's between consenting adults. If you want to sleep with your brother or sister, I personally find that really really icky, but whatever. Just as long as everyone is of legal age and agrees to it willingly, why not?
Just don't ask me to join you.
The Bible, by the way, appears to tacitly condone incest. If everyone on earth is descended from the same two people (Adam and Eve) or the same family (Noah's), then incest had to have happened in the first few generations. Right?