Hmm... I dunno, curiosity is a natural human element, and I think if a family member looked as hot IRL as some of these women do in these games, almost any 18 year old male would definitely notice. Now would they act on it is the question? There are plenty of IRL cases of parent/child hanky panky and there was no 'separation as described. I think some are forgetting that the 'norm' may not be the 'norm' for 99.9% of the people on the planet, but something vastly lower as a percent of the whole.
No offense, but I don't think all of your logic is sound. Incest among humans overall is generally not that high. There are around 7.7 billion people on the planet, 25% of whom are 15 or under. Let's only use the other 75%, to steer clear (mostly) of potential pedophilia (which can also be incestuous and often is). That leaves around 5.77 billion people. So how many cases are "plenty"? If 10% of the population were having incestuous sexual encounters, that would be 577 million people. Does it happen that often? That seems a lot higher than I would expect, but it could be true. But even 10% of the population isn't something I would consider "common".
A part of these numbers are determined by nature itself. If you look at some recent studies, sexual satisfaction among those with more similar genetics was drastically lower than those of dissimilar genetic makeups. When asked to smell random shirts to see who was most "pleasant" and "sexy", another study showed women consistently picked those most genetically different from themselves.
I'm not saying it doesn't happen or that there might not be natural attraction that builds up, but it's not something that is common (though it depends in part on what you consider "common"). While it often is, "normal" doesn't have to be a judgmental word. If someone were to say incest isn't "normal", they might simply mean that it's a different attraction than exists in the majority of the human species. Wolves hunting humans isn't normal behavior, but it does happen in rare cases. Likewise (though far more common than human-hunting among wolves), incest — even at 10% — isn't what I personally would consider "normal" behavior among humans,
in the sense that looking left or right you're bound to find someone engaged in it.
I don't have any problem playing games with incest themes, but none of the renders I've ever seen look similar to anyone to whom I'm related. If they did, I would avoid the game because I don't have even a slight sexual attraction to any relative IRL, even though I think some of my cousins are beautiful. So even though I'm following along with the premise of a game, I don't actually have a relation-based attraction to the models.
I also don't buy that the argument "If I had a sister that hot..." is necessarily true, because you don't actually know unless you're in that situation. My own sister was a beauty pageant winner (so I assume hot), but I never thought of her that way in the slightest. Like you say, I noticed she was pretty, but never anything more than that. Obviously, that type of attraction
can develop for some, but I don't believe it's typical among humans. As Korben Dallas said, a part of that could have to do with nurture from a very young age, but the fact of the matter is that it doesn't seem to be a common trait among humans, not "normal" behavior, for whatever reason.
Whether my own logic about incest is flawed or not, in Second Chance it seems like Nicole is way too anxious to jump the MC's bones. Like, she seems to be having regular (or at least) recent sex with Derek, so it's not like she doesn't get any. Is the MC actually that much hotter than Derek that he's so easily cast aside? He seems to be a good enough dude in general (doesn't abuse her, doesn't fight with her, tends to treat everyone well/fairly, etc.). I just don't see why she's snapped over to the MC and completely cast off Derek. It seems forced, a bit unrealistic to me.