Perhaps its just me but maybe the reason some people like incest games is because they don't really feel like they are in a family? Don't get me wrong i don't mean it in a demeaning way, just from my personal experiences. For example, my mom and i are very close (in a parental way no weird stuff there) so when i stumble upon a mother-son incest game i legit feel disgusted, its a huge boner-killer for me. Now, I don't even talk to my cousins and when i see a cousin-incest story i don't really feel disgusted. I just see it as any other lewd story. So for me since i don't really view my cousins as "family" i don't find it weird at all; but i see my mom as family and so anything sexual about biological mothers disgust me. Just my theory there, not that its relevant to the question lol. Also for me the main focus of the game doesn't really matter, if the writing is good any topic is fine with me.