Your points are valid. But you failed to adress the main core issue. The story breakage that comes from NTR. It's a simple hard fact that adding NTR breaks any story unless it's built around it. Same as the girl. As it simply creates the problem of 'Why am I doing this in game/why does my character have to do all this to get with this girl nad do stuff with her, if it's THAT easy to get into her pants that someone else can just show up and do it?'
Your points are valid but fail to adress this. No matter how you want to spin it, this breaks any games story and relaitonship building as everything feels like a waste of time. As why are WE putting in all this work if it's so easy to have her that someone else can just swoop in?
This is the core problem with NTR that can't be debated.Real or not the STORY itself is damaged.
It doesn't have to, though. It depends on the situation and the writing behind it. Do you really have to work all that hard for that specific girl? Or is she pretty easy for you as well? Maybe she just enjoys sex in general, just like the male protagonist obviously does. Nothing wrong with a girl who just wants to enjoy herself, after all the protagonist is apparently doing the same.
And is the other character really just showing up and getting her with no effort, or does that other character ALSO work hard? Is the NTR/No NTR option specifically about that? Are both characters working for something to impress the girl, and your option there is whether you win or lose to this character, and if you lose to them, they get the girl? Doesn't even have to directly be win/lose, maybe it's all about how you act towards her. Or whether you decide the effort isn't worth it and move on to someone else, and the rival does put the effort in and earns her.
I just gave you situations in which the core story of the game is improved by NTR, not damaged. Your own actions have consequences, your own choices. So stating that NTR always damages the story is just plain silly. Plenty of games have done optional NTR very well without damaging the story, and those games are more popular even for NTR lovers because plenty of NTR lovers tend to like a good story behind their NTR situation as well. There are lots of ways to write out an NTR arc / character that enriches the experience as a whole rather than having it just be cheap and thrown in out of nowhere.
Anyway, I'd say this conversation is about at an end on my side at this point. I don't think I have anything more to add that I haven't already stated in some way or another, so I will likely leave your next reply on read instead of responding again. Don't want to turn this into a neverending NTR debate.