I think something got lost in the shuffle here. The top level comment of this chain was (which is also what the article is about):
imho incest should only be outlawed because of the risk of gene defects during pregnancy. so while nasty I dont think a hanky panky from your first cousin should be outlawed
So in my mind it was always about whether or not first cousins fall into the realm of incest and/or inbreeding. We both agree that there is probably a instinctual component to the rejection of incest. I think that, just like with the rejection of homosexuality, the aversion to first cousins because they're incestual is also conditioned, which is why it shouldn't be outlawed. Although I could be convinced otherwise.