Incest is vile and I doubt people need to be abused to revile it. Pay attention to the conversation. He doesn't want to write that crap and it's understandable, it's his choice to write it or not. It would be nice if he allowed us to be good parents, though, but he's determined to be a prick.
I don't actually think incest by itself is vile. I would compare it to eating your own shit - sure, i'm going to think there is something wrong with you, but I won't think you're an evil person for doing it. The issue is that in real life, it's typically not consensual and it's hard to establish plausible consent due to the influence of power inbalances (parent/child, younger/older sibling) or just the fact that you can't get away from that person easily. Also the issues often surronding it, like pedophillia, grooming, childhood trauma, strange living conditions etc.
Also, he wrote Gwyn, so the idea that he can't write incest is ridiculous. Sure, it's not technically incest, but like, the words are there, just swap the PC for Garth in that roleplay scene. You can't write a brutal rape scene preceded by "All people in this scene actually gave consent" and then claim "Rape is bad, I would never write such a thing." Let's not pretend him being morally opposed to writing incest is the issue - not that I personally want him to, since I doubt it would be what people want it to be, at best you're looking at another "timeskip was your fault" situation.
He can, of course, write what he wants, but he is getting paid for it. Surely you can imagine how his spiteful acts towards the people who give him money would leave a sour taste in their mouths, especially since they can't do much about it if they care about the rest of the game.
Thing is, I find it especially hard to work emotions in writing for CoC2, because I can’t really account for either character; I have to write with a generic protagonist in mind, and since I’m a newbie they want me writing encounters with generic NPCs to start off, so it gets real impersonal, real fast.
You can't write anything meaningful without assuming something about the protagonist. Unfortunately, many writers in this game have their own distinct style, making the protagonist into a schizo with no established morals or preferences (good or bad), like Tobs with the "0 input protagonist who doesn't dare interrupt someone's great monologue", or Skow's "perverted old man protagonist".
I think the solution at this point is to gateway all content behind questioning the player's feelings, something like
Righteous option - pick this only if you have a strong sense of justice ("Stop the evil sorcerer!")
or
Emotionally invested option - only someone who cares deeply would pick this ("Help your beloved.")
with options for each personality. Of course, it could just be like - Neutral/evil ("This isn't my problem"), assuming it doesn't hurt you to do so and doesn't fail a quest where you get the best weapon it the game or something.
The ntr fucking sucks because there's no progression or consequences, no changes in the status quo of the relationship, no hints that things will devolve. CoC2 has no ntr, only ''cheating'' and even then... who does it? The cat? I can't think of any serious love interest companions actively fucking someone else without your permission outside the bee.
There is no NTR in the game. The protagonist would need an established love interest, which, thanks to schizo writing, can only be assumed about very few people. Never mind the fact that, again, protagonist that is down for anything, is okay with sharing and the only reason why characters are monogamous is their choice, not his. Of course, just because it's not in the game, that doesn't mean you, the player, can't feel like you're getting cucked. Think about it. Would you care about Azzyran/Liaden if you couldn't sexually interact with either? Would you care about Brint/Elthara? I think the real NTR is the player feels insignificant in those situations - You want to fuck the hornet? Sure, but here's a character that she likes more than you in every way. You want to knock up the priestess? Sure, but here's someone that can do it better. Etc, etc.