In an interview after the session with The Hollywood Reporter, show creator Epstein kept trying to dig out of this MTV stunt. "Even though there is an incest component, I think the show is not about willing incest participants. How Lucy responds to this information, what she does with it, that's going to carry us into the next couple of episodes and into the series itself."
In other words, the shock of an "incest component" is cynically designed to hook viewers into the show. "The show is not about 'I want you so bad, but society won't let us happen.' ... It's really about telling dramatic stories that are real and compelling and keep us invested in these characters ... It's a great hook to bring you in, but you'll stay past that."
It's too bad horrible plotting devices like this can't just get rejected in the germinal stages at MTV headquarters before the show is made. But MTV will keep pushing social norms to the "edge" and beyond, until there is no "edge" left to exploit.