A day without a needless racial slur is better than a day with. Maybe the comment was ignorant, but using a racial slur to try to undermine it is even more ignorant and needless. It is a misappropriation of power of the word, it wasn't necessary, and is an incredibly disproportionate response.
My initial reaction to your comment was along the lines of
> Do you consider how a black person might feel writing it? It seems somewhat necessary to bring up past persecutions.
I had likened this to swearing to highlight emotional intent. However I have no idea how that word affects some people. I'm just a white guy who is in no position to have an opinion on whether this is okay and was wrong to belittle it.
Words have power and these words are strong. And they should be, because the response is directed at complete ignorance.
This kind of reaction feels quite closed-minded, working on racism-as-a-checklist.