In fictional work the protagonist or point of few character is the one we empathize with the most, which is why something like Breaking Bad is an excellent example, even though you know Walter White is a bad person, you are still more tolerant of his actions than if the show had been from someone else's perspective because you follow his journey.
There's some truth in what you say, a lot of people like it primarily to see the degradation of the woman or the relationship, but then it brings up this question that a lot of cucks in denial don't like.
Why then does the perspective need to be from the guy getting cucked? Why does even need to be NTR and not just cheating? Why does NTR seem to vastly outweigh games with the protagonist doing the cucking to nice guys?
There's an abundance of games where the MC saves the female from a comically uncaring or even abusive boyfriend or husband, which takes a lot of spice out of the whole cheating thing. I have hopes for Julia Miller in Symphony of the Serpent but they've already dropped strong hints that the husband thinks his curvy wife is overweight and this will be you saving her from a broken marriage, corrupting a woman in a working marriage would be hotter.
You both have some great points about self-insertion. His poll is enlightening for me, I'm grateful he posted it. He had a hypothesis, and he tested it out, and came back with useful information. That's science right there in action.
Personally, I don't self-insert myself into stories, which I think is why I dislike Isekais/harem stories. I don't root for the character unless I like them or can relate to them (like you can with other people in real world), but they're often perfect men with no personalities in an isekai, and all the girls jump on him. There's no challenge or relatability to me. I see "self-insertion" as not someone you relate to, but as someone you can see yourself as. In the case of an isekai/harem game, I think you need to lack introspection, and to delude yourself on who you are (yeah ofc my crushes BF/husband is a bad man, how could he not be? I'm the good guy of my story!). That takes a lot of the tension away from me. Where is the challenge? Where is the transformation/character development? Where is the tension? Where the HELL is the plot?
In Breaking Bad, I was rooting hard for Walter White, even though he was the bad guy, and his vices became clearer on rewatches. A lot of what you say still applies, but if he had no uphill battle to climb, or grey area's, I wouldn't have been half as invested. I wanted to watch a challenge, to be on the edge of my seat. I want that tension. That's a great story telling in my opinion.
I don't think that is the case with self-insertion. With harem eroge games, there is no sexual tension for me, because they're the same thing as a porn pic gallery to me. You can skip it all, and it doesn't matter, because I can't relate to Mr. Perfect who gets all the girls even though they have no redeeming qualities. Walter White I can relate to, not because I think I am a genius, but because I can see some of his character flaws in myself (he starts off as a loser), and I can feel emotionally moved by the consequences his actions have on his family (I do have empathy). There's a tension from me made from mixing entertaining feelings and uncomfortable ones, as well as moral grey areas you see in the real world (but in an extraordinary setting), so I loved that show. I get a feeling self-inserters won't enjoy a show like BB because they don't see themselves as the bad guy - it's a lack of introspection. Which makes the cuck self-inserter a more interesting psychology, particularly the netorare ones.
I also totally understand why many netori games are boring. If a netorare game let's you view it only from the female's perspective, I usually choose that one, because I enjoy the taboo nature of it (which creates tension), as well as the psychological corruption. With your netori examples, it can sometimes feel like excusing sh*tty behaviour in order to still be the 'good' guy. Men do this in real life when they have a crush on a taken girl, they can find an excuse that the bf/husband is a bad person, when the truth could be, that them and the woman* (if she's led him on) are the real baddies of the story. Even if the bull was a d*ckhead, I don't think I'd enjoy half as much, because there's not as much psychological conflict from the woman's POV (harder to explore it), which in turn creates (sexual) tension for me. I enjoy watching a woman become more corrupt, and the more realistic that is, the better. So, if it hits the corruption part for me, it does the job I want.
A lot of isekai lovers dump on NTR, but I think Doki Doki Literature Club does a good take down of the immorality of those kinds of stories. Whereas NTR is often cruel, it knows it's cruel, and has an understanding that women aren't cheap and have a complex set of feelings (the best ntr understand this). Isekai/harem stories treat women like they're sluts, ready to jump on your D, and not bothered in the slightest whether the love of their life sleeps with 100 different women. There's no regard for how someone other than yourself feels. It's easy thinking you're the good guy, but not so easy thinking you're a Walter White... but without the genius. In the real world, if the self-inserter in a isekai was living out their fantasy, they'd hurt a countless amount of women in the process, but many don't seem to realize this. There's a difference between relating/emphasizing and self-insertion. What you're self-inserting into, also says something about you too.
I hope I didn't waffle on, but you added to a great point, with another great
