Oddly enough, "TheOnlyWordThatWouldGetMeBanned" came first. Then came the reasonable, 20th-century idea that we were entering a new era of more cosmopolitan respect for black folks. It was thought that we therefore needed a new word, inasmuch as "black" seemed stark and rude—which it is, if you happen to think there's something wrong with being black. Which the educated elites still did. They started substituting "negro" for "black," "colored" and less polite terms. To the elites, "negro" seemed more polite than "black," because it was an exotic, technical-sounding, foreign (Spanish) word . . . for black.
By the time I was a kid, southern whites had adjusted this to "nigra," which began to sound a lot like TheOnlyWordThatWouldGetMeBanned.
And of course, in due time, "Negro" became anathema to young black firebrands, because it reminded them of old black firebrands, to whom they felt superior, because the old ones went to church, and they didn't. You know the rest: Afro-American, black, African-American . . . and whatever is next. If you're in the grievance business, the term of 20 years ago always seems tinged with bigotry and surrender.
I don’t see how that’s quite true. “Negroes” was being used way back on 18th century broadsides advertizing for slave auctions. It has always been a “proper” (as opposed to slang) word for blacks as far as I know from history, and was around a very long time.
As far as I can see, “negro” went out about 100 years ago, defintely by the ‘40s, and was sort of replaced by “colored” (my gramma referred to them this way). TOWTWGMB was always a slang or slur term, never proper.