Really messed up someone would make a game about incest. Sick shit people make and put on places like this.
You must really hate Game of Thrones then (or any other type of fiction that depicts this topic). First, it's not real and all fantasy (which is fine). Second, how about all the games were you go around killing and murdering people? That could be considered sick as well and yet that is considered perfectly fine (most of the time), because NONE of it is REAL! Get what I'm trying to say? Playing this game does not make me want to go out and bang my real sister, just as playing a shooter doesn't make me want to go out and kill people.
And as khairus mentioned, if you don't like it, then don't play it and move along to stuff you do like. It's really that simple.
Murdering, Raping, Sleeping With Your Family, none of it is Relevant if they're 1s and 0s Binary Code. It's a FUCKING Fantastically Fantastic Fantasy. VNs are porn. You read the story, you "use" the pictures/scenes, just as you would if you typed "extremepussyfuckingstraponlebians.cummm." Unless SKYNET (Terminator) takes over (Then Every human is raped anyway) it DOESN'T MATTER. If you like pissing, lesbian squirting, or gays ass fucking each other, you download anything IF YOU DON'T, don't download it or if you DO then press SKIP past the (offensive) material. It's kind of self-explanatory and logical.
Having a "Special relationship"... Sneak into her bedroom at night. Watch her sleeping. See her perfect breasts rise and fall. A cute little smile on her face and wondering what she's dreaming about. Then you slowly lift her night gown. "Ohhhh, Mommy, I want to see you delicate pussy lips"... Or "Mmmm. There's my 18 year old Virgin little sister. Oh good, you're sleeping on your stomach. I need to spread your cheeks and lick your asshole *lick* *lick* *lick* hmmm. Looking at each of them as you leave: "I can't wait to Impregnate my beautiful girls"... There you go JD. How do like incest now?...