I'm taking you in good faith here, despite being warned that you're a possible "wrecker". I have been convinced that my post (where I tried to make clear that I could easily be wrong) was incorrect about the origins in english.

I think what we're really getting at here is a difference between some of what constitutes a psychology which is deserving of protection from incorrect associations with acute attributes found in broader populations. The R word clearly describes something which cannot be described as "traits everyone has but this person has more of it" but is instead taking a broad and incorrect category and using it to demean both the target and those who are neuro-atypical. With Narcissism, it seems that those in favor of using the word broadly are really then taking a stand that NPD exists as just an extreme of the scale of narcissism and is, therefore, to be less protected. I am unconvinced of this argument, or at least not convinced that, even if it were true, the word "narcissism" is really necessary outside of medical contexts. I think this is unpopular on hexbear based on the posts I've seen, but I'm fine with stopping using the word outside of describing possible the specific psychology.

I think an interesting thing to consider though, which doesn't discount this argument, is the social situation which leads to the commonly used terms. Anxiety was a term used broadly to describe a spectrum of anxious traits in the middle of the last century and was for the first time made primarily psychological instead of sociological. The same can be said of despression in recent years. I think that narcissism as a psychological disorder likely also has a base in liberal capitalism which has only gotten more acute, and it may be less widespread and blamed on failures of society once we move on from this terrible ideological base

The separation of 'derogatory' and 'patronizing' as your link shows is not a difference in it being a slur or not, but a difference in social understanding of the word. It was always a slur

edit: I say this not as a disagreement about the term narcissism, but that it's comparison to the N word seems unfounded to me and not related, maybe even downplaying the relative harm of the N word.