Smeatza said:
That is interesting but I was thinking more in a general sense than in regards to sexual deviation.
For example. A child born of an incestuous relationship is significantly more likely to have genetic defects.
And if a family accepting incestuous relationships as normal, increases the likelyhood of subsequent generations having incestuous relationships (not saying it does just my example), would that not make the chance of an incestuous pregnancy (accidental or otherwise) happening much higher?
If it was culturally accepted en masse wouldn't the amount of babies with defects being born rise significantly?
Oh, so when you said "the psychological aspects of incest", you meant "the psychological aspects of inbreeding"?
Well, first of all, the former desn't necessarily assume the latter. It's not difficult to imagine a society where sex or even long term relationships between siblings are accepted, but inbreeding is heavily discouraged. Birth control technology is already pretty safe, especially the long term solutions that would work for spouses.
Second, there is the Westermark effect. Right now, incest is discouraged by both the effect and by taboos, while encouraged by the Genetic Attraction effect, and by the emotional effect of long term intimate relationships. These four add up to incest being extremely rare. So even if we would take out the taboos, probably the Westermark effect would be strong enough that incest would be somehow more common than now, but not as significantly common as natural attraction between people close to each other would imply.
Third, I think you are misunderstanding how genetic defects from inbreeding work. Real life is not like Game of Thrones, where every time an inbred baby is born, the gods toss up a coin and it has a 50% chance of growing up batshit crazy.
Inbreeding can trigger a number of pre-existing hereditary disease genes that the two relatives shared. If they share such genes, their child is extremely likely to be born with that disease (e.g.: Huntington, Hemophilia, etc), and if they don't then their potential children are safe. These genes can be tested in advance nowadays.
But it's not as simple as children resulting from incest getting some sort of vaguely defined "negative psychological effect".