What people attribute to what upsets them about political correctness, however, is precisely what has been used by groups from centuries ago, for various political and social causes.
It is terribly fascinating to see it play out in the press in the immediate aftermath of the Denmark Vesey incident. South Carolinian papers identifying specific papers of the North, specific authors, who had broken the "long-standing" social custom of observing the sensitivities of the South's slavery regime. Then immediately in regard to the abolitionist literature in the post office episode, when the mere act of having mail addressed to you which offended Southerners (a numeric minority, with a white demographic majority in the nation--but sometimes nevertheless minority status in a given county) could be reason enough to be socially ridiculed, isolated, or denied access to information. Words were heavily regulated, and only the right words or tones were accepted.