From Louis Menand’s New Yorker essay on literary books banned for obscenity:
“The term “obscene” is a conundrum. Is an expression obscene because it’s arousing or because it’s gross? Is the relevant affect lust (a pleasurable feeling) or disgust (an unpleasant one)? Brennan tried to split the difference with a new term. “Obscene material is material which deals with sex in a manner appealing to prurient interest,” he wrote.
The Supreme Court had used “prurient” only once before in its history. That was in Mutual v. Ohio, decided in 1915, when the Court held that motion pictures are not protected by the First Amendment—the decision overturned in the Miracle case. In Mutual, the Court noted that “a prurient interest may be excited and appealed to” by movies, but made no more of it. Brennan cited Mutual, but he saw fit to add definitions of “prurient” from other sources as well: a “tendency to excite lustful thoughts,” a “shameful or morbid interest in nudity, sex, or excretion,” and an expression “substantially beyond customary limits of candor.”
Possibly sensing that the scattershot nature of his definitions simply provided prosecutors with more weapons, Brennan tackled the problem from another direction. He defined what would not count as obscenity. “All ideas having even the slightest redeeming social importance—unorthodox ideas, controversial ideas, even ideas hateful to the prevailing climate of opinion—have the full protection of the guaranties,” he wrote. “Implicit in the history of the First Amendment is the rejection of obscenity as utterly without redeeming social importance.””
I wish Menand here had mentioned an earlier notorious incident in this history, Judge John M. Woolsey’s 1933 decision to allow Joyce’s Ulysses to be published in the United States. Woolsey’s reasoning is superior to that employed by Justice Brennan, and some of the later arguments that Menand describes could have been handled more effectively if Woolsey had been more frequently invoked. Woolsey demonstrated that the laws against “obscenity” are misnamed: they’re really meant to be laws against pornography. If you look at their contexts, such laws are always seeking to ban books that arouse people sexually. But for Woolsey, who thought about these matters philologically, “obscenity” is a much broader concept and may not even overlap that much with pornography. He argued that pornography has one main, usually exclusive, purpose: sexual arousal. But one may write an obscene book — an offensive, a shocking book — for many reasons. (For instance, Swift’s “Modest Proposal” is obscene, and obscene in a righteous cause.)
So, Judge Woolsey argued, to the question “Is Ulysses obscene?” the literally correct answer is Yes. But the laws do not really mean to prohibit the publication of obscenity — they use that word carelessly and inaccurately. They mean to prohibit the publication of pornography, so the proper question to ask here is “Is Ulysses pornographic?” And the answer, to Woolsey, is clearly and obviously No. Therefore, he ruled, Ulysses may be published in the United States of America.
It was a decision both brilliant and correct, but because its logic had been largely forgotten by the time of the trials that Menand describes, those debates were muddier than they had to be.
Maybe the problem is that already by Brennan's day the idea that there was a legitimate public interest in regulating sexual arousal had collapsed, though we didn't know it yet, so Brennan had to resort to all sorts of strange illocutions to acknowledge that fact without quite giving up the ghost entirely.