What is it with light novels and incest?
Japanese culture is notoriously lax about all things sexual and at the same time very repressive in general, so we see a lot of pent up aggression, sexuality, sorrow and other emotions a japanese person is not expected to show in his daily life expressed through manga and anime in particular and pop culture in general. If those poor salarymen didn't (make it look like they) work their asses off every day of the week, the stuff Japan churns out would be significantly less crazy.
The best way I like to put it...
Is that Japan is a very repressed country that at the same time fully believes that those things are best done behind closed doors.
Unlike lets say America where during the peak of its... lets say... Sexual Repression was against anyone not having sex in a very specific way closed doors or not.
---
Actually on the subject of Japan, I find it fascinating when a uniquely Japanese Aesop finds its way into an anime (or at least non-western Aesop)
What do I mean?
For example one episode of an anime's Aesop was about "fitting in, in a foreign country" and was that "You should act the way everyone else acts in order to fit in" (and no, it wasn't a give and take such as acting in a similar way they do in order to be approachable). It honestly felt like I was being told how Japan honestly expects foreigners to act in their country. (to admit I could be misinterpreting... even if "the American" is as much of a cartoon as the "Asian" is in western media)
In Gamera, while this is outdated and I am sure Japan doesn't think the same way now, the Farmers in that movie were the villains because they were holding out against the government so they would get more money for their land... Honestly my mouth was gaping when that line was dropped.
Which honestly astounds me because these storylines would be unthinkable.