'ntr' is indeed the dumbest thing, but it's not about its use as a tag, it's just an extremely unfit-for-purpose loanword. Trying to stuff at least four or five things that are completely separate in Western conception into this one Japanese concept. I can't understand why people keep using it. I've seen multiple examples of fights breaking out over whether it's being used correctly, all of which could be avoided, and time and effort saved, if the person just said in English what they were referring to instead of using the term 'ntr'. That's achieving the exact opposite of what a loanword is meant to do.
For tagging itself, on blogs/forums without much user feedback, yeah, it's just SEO stuff to drive clicks. I more or less completely ignore tags on those places. For effninetyfive and here and places like that, there's a built-in tension where some people mainly use tags to avoid content they don't want, and some mainly use them to find content they do. imo this is why you end up with stuff like games getting the 'ntr' tag because MC's big sister's best friend once held hands with a guy etc. People demand the tag be added because they want a reminder to stay away. So people who want the shit cucked out of them find the tag's attached to a lot of stuff that doesn't interest them at all.