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However, it is morally wrong if it's between a parent and a child because the parent holds power both emotionally and psychologically over the child, making it non-consensual, and therefore rape.
There is a greater risk of abuse in these relationships. Power dynamics are much more complex. Age of consent would be especially important in these sorts of relationships to ensure that both parties have enough life experience to keep the relationship healthy and consensual.
I think you should clarify or remove the "socially" part from the premise altogether. Almost every society on the planet considers it a taboo (as the other person said). So it is "socially wrong" in a way (what you postulate is kind of fuzzy), but I have no moral objection to it.
There is still something socially wrong as it's still taboo. But nothing really wrong morally. The dislike of it came from when you'd pop out retarded (aka "demon") kids from it. Biologically it's a no no, but not morally a no no.
Every human being has a right to love whoever he or she loves.
Love is an unstoppable emotion
Any children created via incest are more likely to be born with mental handicaps. Knowing you are more likely to have a child who is mentally retarded if created through incest is just as immoral as smoking or drinking while pregnant.
It may not be immoral, but there is value in our society to having social norms for explicitly platonic love. Especially with children and their parents, children will likely not feel as safe and comfortable in their development when there is the possibility of romantic love with a parent.
You might kill your dad and then gouge your eyes out like in Oedipus Rex