Can't say I've looked too much into hentai. I mean the first (and almost the only one) NTR I've ever even looked at was called NTR Kanoko - Suzumori Mizuki written/illustrated by Satou Kuuki. This was literally a little over a month ago, so just know my knowledge on hentai in general is severely lacking. Can't say I look at much of it. I also only looked at it because someone sent me a link and for whatever reason, declared that it was getting a hentai anime adaptation. I'd almost swear the guy was promoting/advertising it to me for some reason.
Anyway, aside from the forced situations, the logic of NTR is hilariously amusing. I mean, from what barebones little I know of all NTR situations, it seems to me that they would end in real life with someone calling the police, telling their (apparently normally a male) lover/husband/etc. what was going on, or just flat out saying "fuck you" before the actual NTR sex scenes would even begin. So, to me, the NTR genre, in general, is extremely unrealistic and illogical because, from my outsider POV, the whole thing could be easily avoided. Like the one I mentioned here, the whole situation could have been avoided by literally calling the police, leaving the camp, or just flat out speaking to someone at the camp the first time the dude even looked at her funny. And since women tend to control courts nowadays, just cry a little and they almost always win the court case against a male defendant, NTR just isn't realistic.
Idk. I can understand the hate if someone has experienced infidelity, or just in-general has trust issues, but otherwise, I can't say I get what the problem is.
It's like polyamorous relationships I suppose for me. I find them disgusting, and while I don't go out of my way to shame them, I have no good feelings for them or the people who engage in them. But that's their business and I rarely find the time to talk about them or even think of them. It should be the same way for people who dislike NTR. Dislike it, but don't bother thinking about it if it bothers you.
Personally, yandere is far more upsetting to me, since I've had in my dating history, more than one ex-girlfriend that turned crazy-obsessive and ended in life-threatening situations.