If you watch reruns of the Brady Bunch, when Marcia and Greg are fighting about who gets their own room moving to the attic, there might as well have been cartoon bubble hearts popping between them.
The actors were dating in real life, but it occasionally came through when playing Marcia and Greg. Even though you knew that it was a story about a man named Brady with 3 boys who married Carol and welcomes her 3 girls into one new family, Marcia and Greg simply step children with no blood relations at all, you still went, "um, Greg??? Marcia.???? Um, uh, don't they have other kids at school so you wouldn't look like you were longing to kiss your sister??"
I think most of us are repulsed, because we think of ourselves getting busy with our sibs, and it just makes you want to pluck your eyes out. You also fear that your neighbors will be like that episode of the XFiles, called Home, where the brothers had the same mother as father, who was also their brother, and they were all creepy deformed...
I often wonder about things like Sperm Banks. If a guy goes there all the time, and women use the sperm for babies, there is a chance, that his daughter may fall in love with his son.
To me, I am only concerned about the inbreeding mutants. Other than that, I read Flowers in the Attic in HS, a cheesy paperback where a mother who apparently fell in love with her brother, was disowned, but when her husband died, she returned to her rich family asking forgiveness, and asked the kids to wait until the time was right, by living in the attic. They waited for years, the mother visiting them less and less. The older boy when through puberty, as did he sister, and having no other contacts, they fell in love.
In the context, it wasn't at all icky, but more on the "what about when you have mutant babies??", and asking this about the beautiful, blond, blue, Aryan Nation kids.
I think it is fascinating to hear people, trying to illustrate that God is anti-gay, because he created Adam and Eve, and not Adam and Steve, to follow that through:
Adam and Eve, had Cain and Abel, and bunch of other kids....
And then.....
Incest.
I then ask, "did God not see that coming, or is it, as you claim, God's plan, that Eve be made for Adam, that they have kids, and then their kids breed incestuously? And if we are to follow God's plan of heterosexuality only, should we not follow through on telling your kids to marry and reproduce?
I don't really believe that, and honestly, I have a problem believing that Adam was one guy, and Eve one woman, and that is how the entire human race came to be, ignoring the Indians of the Americas who Christopher Columbus discovered...kind of....even though they were already there...
But I doubt that most Christians really get to the 3rd Generation, because of the ick factor.