Argument: Incest is taboo without a clear rationale as to why
"Old Incest Debate Gets New Blood". Queerty. May 3, 2007 - For centuries, man has fought against familial love: the last taboo. The mass revulsion over incest, as Jacoby points out, comes more from its "ick" factor than any clear and present danger. It seems to us that the legal system's sexual double standard compromises its legitimacy. We may not personally approve of incest, but it seems to us that if a brother and sister or mother and son or grandmother and granddaughter want to get it on, they should be allowed. Yes, it's may be a bit distasteful to much of the population, but so is anal sex.
"Sexual Ethics: Consensual Incest". A Nadder. October 13th, 2008 - If you keep a moral belief only because of moral disgust (meaning it's unjustified), it's therapeutic to at least acknowledge it. I have a belief that [consensual] incest is disgusting and wrong. The paradox is that I know this is false, that there's absolutely no reason to believe it. People go absolutely apeshit over incest (see a thread I started years ago just to see what people would say). But the arguments can be refuted by a hamster:
[...]Anything producing moral panic should be viewed skeptically. People even feel a need to verbally state "that's sick" to incest stories from the news, as if to make sure everybody knows they don't approve. Even if you agree with the arguments-from-disgust, consensual incest isn't the end of the world.