I would think,
1) My partner has no concept of self control when it comes to being a member of society and begin to question what other social norms they can't grasp like washing their hands after going to the toilet.
2) What sort of loser can't get a date in a population of 6 billion that they have to resort to their sibling ?
3) Should I start to worry if we have children that they would then consider child molestation one of these moral "rules" that should be ignored?
4) Remind myself to constantly check their browser history because just as murderers usually have an interest in animal abuse, incestuous humans no doubt have plenty of other sick sexual fantasies that would no doubt repulse me just as much.
I strangely have just asked these questions - its pretty much impossible to answer. Yes I know ethical debate is one thing - but what would we actually do given this option? (reminds me of the movie 'after the dark'). Arrrgghh - shakes fist at ChipTrippyFox