Ultimately, it's just a stupid rule of Patreon. I mean, I'm not a fan of incest fetish. Just the thoughts of banging my mom or my sister and I have the urge to gag. My mom and my sister are really nice persons but fucking them? Hell, no! But after all that's nothing you should ban a book, a movie, a game, you name it for. We clearly don't need incest in games, but if some devs are into that and wants to make a game for a little bubble, why not? There's no harm. What people do in their bedrooms by mutual agreement is none of the society's business. So why should something like this be banned? It is important that both sides do it of their own free will and without any constraints.
But again: incest would make this game weird and destroy it. It's a good story because all of the characters seems to be "Intertwined" and about the drama with that. There's no need to let MC fuck his own mother. It just doesn't fit to the characters of Emily and MC.