True, but it was also the preferred term used by anti-imperialist black leaders for most of the 20th century. Read anything by WEB Dubois, Malcolm X, Robeson, Nkrumah, MLK, etc.
"One of the reasons that it is bad for us to continue to just refer to ourselves as the so-called Negro, that's negative. When we say so-called Negro that's pointing out what we aren't, but it isn't telling us what we are. We are Africans, and we happen to be in America. We are not Americans. We are a people who formerly were Africans who were kidnaped and brought to America. Our forefathers weren't the Pilgrims. We didn't land on Plymouth Rock; the rock was landed on us. We were brought here against our will; we were not brought here to be made citizens. We were not brought here to enjoy the constitutional gifts that they speak so beautifully about today. Because we weren't brought here to be made citizens--today, now that we've become awakened to some degree, and we begin to ask for those things which they say are supposedly for all Americans, they look upon us with a hostility and unfriendliness" -Malcolm X
What is even your point? If a non-black person walks up to a black person in America and calls them a "negro", it is likely going to have the effect of any other slur. That's the reasoning for the content warning. The fact that it wasn't a slur at the time of its use in this leaflet is relevant for context, but in the context of our modern world, a lot of black people don't want to be called a "negro".
If OP changed the title from "the N-word" to "an N-word" would there be less pedants in this thread?