I have seen a couple posts on whether incest is moral or immoral. I have read through a lot of the comments and I think there is a giant point missing. When we have a situation of two adult siblings wanting to have a romantic relationship, when is it do you think their feelings formed for each other? Do you think upon their 18th birthday, they finally saw attractiveness in each other. Same question for a father/daughter or mother/son situation. Do you think the parent became attracted to their child only after the child became an adult? Because why would they.
At the very most either set of couplings have spent 18 years together. Especially for a sibling situation, feelings of attractiveness have probably stemmed from misplacement of sexual energy during puberty and adolescence. The roots of their now adult relationship started long ago. Same thing for parent-child relationship. Can we promote that it is okay for an adult to want their child sexually as long as they don't act on it until their child is 18? Does that sound healthy?
The reason we have family is to have a set of lifelong human connection and protection. The bonding from sex changes dynamics that take away from the purity of love siblings have for one another or a father has for his daughter. There a millions of people out there, let your family be your family. And for those who did not know they were related by blood before meeting, know that the bonds of family are much deeper than that of blood. You cannot change what you did not know.