Lol wtf are you even saying here. Fag.
1: Love SICK is all written with actual skill, as opposed to the porn shit that people write with one hand over the course of like, a half hour.
2: The point of the story isn't fantasizing about fucking your sister, it's the inherent humor found in the shock factor there. It wasn't written for degenerates who actually want to nail a sibling, it was written for normal people to read and be delightfully disgusted by.
It's satire, and if you can't understand that then please keep yourself out of the gene pool (not that this was ever a concern).
And you won't understand any of that, but I wanted to try.