Like I said before in most anime incest is fake and that is what makes it comical...
Personaly I don't find that even remotly funny or comical...
Many anime has fake incest to boost the comedy and eventualy caracters involved in such acts get married or romanticly conected...
If you consider that to be only fiction and nothing of that actualy happening in real life it's just entertainment for people who like strange stuff...
As many other people I see this as harmless entertainment...
btw I actualy do not watch that stuff...