Is incest immoral? If so, why? If not, why not? If incest IS immoral, how far out do you have to go before it’s ok? If brother-sister relationships are wrong, how about between first cousins? Fifth cousins?
I’d be interested to hear what the legalities are. What are the laws regarding incest in the USA? I have no idea what they are. What about polygamy? The Mormons seem determined!
All anyone can efficiently legalize is marriage; sex is always nearly impossible to govern. In the US, brother-sister marriage is illegal everywhere. Marriage to your first cousin is legal in about half of the states, and marriage to further cousins is legal everywhere.
It’s all very confusing.
The children of your parent’s sibling’s children’s children are your ’ first cousins twice removed '.
But…
The children of your great-great-uncle / aunt are also your ’ first cousins twice removed '.
[size=84][ Personally speaking… if ’ Liv Tyler ’ was my older sister… I mean… as long as you use condoms to prevent mutants. ][/size]
birds will not mate with their own families.
Pandas won’t mate at all! 
Incest is cool, but best use birth control 
You know, this is quite an insane question.
Here’s the answer.
Having sex with your sister is just wrong.
The end.
Nice questions.
In one hand you have pleasure leading to procriation (primitive layer of the brain).
In the other you have Ethic (neo-cortex).
What you create with that question is the very essence of evolution. Have we already bypassed sex by ethic?
I think not. ‘Why?’ is another question.
IMHO, I pick the genetic approach, that is, offering more survival (thru a stronger genetic code) probability. By that, you can look to incest has something that will not bring you evolution.
Ethical codes, deployed by society, magnify this science explanation (by other words of course).
On the other side, Incest exists because Ethic Codes are inadqueate to the human condition. In short, they limit your creativity, establish icons like ‘Hell’ and ‘Heaven’ that disrupt the Ethical mind once ethical breaks occur.
I believe that submitting an Ethical mind to ‘unethical’ experiences, generates and overload of preassure (trauma?) which will generate a bad ethical side in that same mind. Like a second personality.
You still have a black and white CRT monitor? …