I disagree with the notion that "ntr" is an entirely new concept.
There has been a historical tendency of romanticizing cheating and affairs for a LONG time.
From a religious standpoint, like how Aphrodite cheating on Hephestaus with Ares in Greek Mythology, was portrayed by many Rennaisance painters as some hot steamy love-affair, and not as a plainly bad thing
To the medieval concept of "courtly love", which was practically straight up just sexualising knights banging married noble women. This "genre" was even concidered to be mostly a good thing for a long time, before it fell out of favor. (Hence why Lancelot got pushed out of the "ideal knight" position by Galahad, in Arthurian mythos in later years.
To just a general prescedent found in many cultures, especially those with pologamy, of a thought that "better men" will win over women in the end.
It's not new, and humanity has a complicated history with the idea.
And not to be the bearer of bad news but most men also agree that murder is pretty bad outside of fiction, so your argument doesn't really hold together. I think the comparison is more than fair.