These are Fantasies not reality.
You answered yourself here. That's just not their fantasy. Nothing to do with any underlying issues. Imagine saying someone " Hey you don't have this particular fantasy? So you're just weakminded and have emotional issues? " LMAOOOOonly the fact that the women is fuckin someone else instead of the fictional MC who they are pretending to be is what makes them offended.
Shitting about NTR in a NTR game is dumb and pathetic. But asking "is NTR avoidable" in a game for example "A Mother's Love" doesn't mean these people have any underlying issues. Because NTR with Nicole will just make that game from gold to copper.
And yes I've seen fair amount of people asking if there's any forced sex in many game threads and if so they'll avoid that. And incest games make it pretty clear from the description/title so the dislikers don't need to ask about it.