skizziks

I'm posting here because to me this is a philosophical question.

When I'm talking incest, I DO NOT mean rape, forced incest, or any of that.

In this instance, when I talk about incest, I am talking about mutually consensual sex between immediate family members.

I know children of incestuous parents can come out unhealthy and fucked up (royal family. west virginians) (calm down, it's my lame attempt at humor in the middle of a serious question), which is, I assume, the main reason incest was outlawed. Trying to keep people from peeing in the gene pool, cross breeding makes healthier stock. Mutts are usually healthier than pure breeds.

I'm talking about sex for fun.

For example, a brother and sister, both adult, have sex for fun, not procreation. Why is that wrong?

If a brother and sister were separated at birth, given up for adoption, met 20 years later and hooked up, not knowing they were related, it wouldn't matter. But suddenly, because they grew up together knowing they had the same mother, it's wrong. Why?

What about all the men with their oedipal complex who frequent the incest porn forums?

I don't think it's a natural disgust. I think we learn it's wrong.

So, why is it wrong?