I'll compare this to another issue: You know how homosexuality has been proven by all non-religously funded science to be harmless? And that kids from families with gay people or gay adoptive parents tend to be very happy and healthy? And there are just (adjusted for proportion) just as many long lasting monogamous gay relationships as heterosexual ones. The gays are accepted cause science and empathy make it clear they're A-okay. If they have problems, it's not because they're gay.
Incest doesn't have that kind of track record. Biologically and psychologically there seems to be real harm. There is some debate, but power imbalance will almost always be present with Older-younger siblings, or parents having sex with their kids. In this sense, how consensual is it? 18 year old daughter and 49 year old father...I hesitate to say the daughter has a lot of power in this sexual relationship. It can also lead to a lack of division of relationships, extreme promiscuity without protection. Not just healthy sexual liberality, just the need to consider everyone a sex partner. This shatters the divides between friend, brother, and fuck buddy, leading to issues forming lasting bonds and forming confident social bonds based on things outside of sex. It's hard to find statistics on this, but people involved in incest are often very promiscuous, to a physically dangerous extent. Because to them, all relationships become sex-based. These are case by case studies obviously, but I can't find many to say someone is happy after having incest.
Abuse victims consistently show signs of depression, and even before kids are taught about 'the places under their bathing suits', they still consistently report feeling great discomfort and fear and intimidation after molestation, long before sexual thoughts are in their noggin in a meaningful way. In addition, their are the natural downsides of unhealthy children consistently produced via incestuous conception.
Maybe someday their will be some exception to the rule. But I can't find any reports about them. There may be bias in this research, of course, and for some, there definitely is. I personally think it's very dangerous, and will almost always be harmful in many ways to both parties, especially the younger. I only say this because I see very little evidence to the contrary. I'm an atheist with very flexible morality based on science, rationality, empathy and love for my fellow man. I'm going off nature, science, study and a dash of gut feeling. I genuinely think touching your sister the wrong way is going to mess both of you up later.
