Just notice that at every link in that chain of events, public discourse was dominated not by efforts to persuade or debate anything on the merits, but by attempts to cast, locate, or portray the target of one’s opprobrium as out of bounds.

The lesson isn’t that stigma is never appropriate. If someone incites violence against Jews or Muslims, for example, the words ought to be summarily condemned, not fodder for debate about whether violent attacks are, in fact, desirable. Still, this episode illustrates that when the constant focus is on the boundaries of legitimate speech, little time or attention is left for substance. And what’s said to constitute bigotry keeps expanding without any apparent limit.

Nowadays, the journalist Damon Linker observed in The Week, “the point is less to convince your opponent that she has made an error of reasoning or is wrong on the facts as to convince your own side, as well as the dwindling crowd of neutral observers … that they are excused from having to take your opponent seriously because she has crossed a line beyond which people shouldn’t be granted a hearing.”