prolonged discussion that doesn't need any extra input but my take on the subject is as such: it's natural that people would have a knee jerk reaction to NTR. we almost always forget cheating and cuckery is a niche thing, much like latex or inflation or whatever genre you might find if you wallow in the filth for long enough.
problem about NTR is with its presentation. rather, it's lack of any special presentation. see, with pissplay or scat or any other niche fetish, there's always something visual that deters the uninitiated. you see a chick pissing in some guy's mouth, you just walk away. it's easy. for NTR, not so much. on the surface level, it's about the same as regular vanilla hentai. a chick gets fucked by either one or multiple dudes. and since hentai is a visual medium, people won't suspect a thing since the initial visual deterrence isn't there. they just dive into the trap head first without any caution. this isn't a detriment to the genre, but an inherent risk it carries.
and before you mention tags, need i remind you that the general audience in hentai consumption, or any media consumption, more often than not, don't read the damn tags. which is why sometimes you see some guy complain about gay stuff happening in a harem webnovel DESPITE BL being in the tags in the first place, or some shitting on an author for making the MC a "weak beta male" despite that giant bold [Weak to Strong] title on the start. with that in mind, it's not unfair to assume most people see the big tiddy married milf on the cover and go in there blind without even giving a glance at the giant Cheating warning hanging over the front door.
as a result, common readers get enticed expecting a fun-loving sexy time only to walk away with a confused, frustrated boner. i mean, they walk in relating with the protagonist/male character and find said character, and by extension themselves, get cucked by Chad McThunderCock. only THEN do they noticed the NTR tag. now, if most NTR start with the perspective of the Ugly Bastard themselves, the reaction wouldn't be as widespread. the cheating is still there, but this time, the reader themselves are doing the cheating, cutting the bad taste in half. BUT, that's not what NTR is for. NTR is for lads who get the stiffy when they see their trad wife get railed by Jamal from next door while he peeps from the closet yanking his microdick.
as a result, NTR becomes this knee-jerk bad no-no thing in the general consciousness. is it stupid? yes. you walked into the NTR hentai, why are you getting mad AT the hentai? go learn how to blacklist tags. still, the general public is what the general public is; a fickle.
it is what it is, sadly.