As an NTR hater myself, what I hate is random NTR jumping at you right at the get go and you can do shit about it. Self-insert is, for some, unavoidable when reading so... Can't really blame them. And the devs says "no NTR" now normally means no sudden 30cm black dick NTR bullshit. It's just how jap devs and many think nowadays. Doing bad things and getting yourself cucked is one thing, but suddenly getting cucked is another. So the "No NTR" warning is actually quite needed.
Also, along with the "sudden NTR" event, most just make the MC a wimp that sat there doing nothing. As someone who got cucked myself (because the other guy is richer than me and, as she said, "manlier than me even in bed"), I can guarantee, the miserable feeling only last until you sleep. Waking up and everything will return to normal again. Yes, I may loath them, but it's not like I can do anything about it. Better just move on (also, I made sure to be a dickhead and spread this matter to the whole school. The female side aside, most of my friends helped me spread this to ruin their social life. All the school more or less avoids them now. Especially those who are in a relationship).