RJ once again it was an honest question. I'll take your word for it that research has shown this to be the case. 923 and Legendz have done you a huge favor by coming in and making the arguments you failed to make on this thread.
923, that was a great post. I do have a couple of questions though.
1. You say that society as a whole has made the judgement that incestous relationships, even those that are same sex, are likely to involve the victimization of one party. To me that involves a non-consensual relationship and thus falls in the same category as pedophilia. I wasn't really talking about non-consensual relationships and was talking more about a hypothetical consensual relationship between two brothers. You seem to be saying that research shows this doesn't exist. I would still assert that many would view that hypothetical relationship as immoral and that moral judgement would be the same as a moral judgement against homosexual relationships.
2. It seems that the arguments against incestual marriage center directly around incestual sex. This seems to imply that sex is central to marriage, at least in the case of incest. It seems that arguments surrounding gay marriage seem to downplay the centrality of sex to marriage. Would be interested to get your comments as to why this is.