Interesting comments about the Japanese comic "Bunny Drop" on the following thread. http://www.animenewsnetwork.com/bbs/phpBB2/viewtopic.php?t=267250&postdays=0&postorder=asc&start=30 It is a series that describes a girl who grows up as an orphan and later decides to marry her caretaker.
I admit I have not read the series, so their may be valid criticisms of it,but I find it noteworthy that people are disgusted with a fictional marriage without blood relations or an intrinsic expectation of sexual perversion. So many of them would comfortably accept a homosexual marriage, but not this apparently. And everyone very nearly treats this as equivalent to paedophilia despite the fact that it is between two adult individuals.
I think this demonstrates an urge to find perversion somewhere, to explain human uneasiness. If it cannot be found in the locations that previous generations would have known new places will be found.