The much-anticipated October opening of “The Birth of a Nation,” the story of Nat Turner’s 1831 slave rebellion, is now clouded by past rape allegations against director, writer and star Nate Parker. Already, critics are lined up against the film. In a New York Times op-ed, Roxane Gay declared she won’t see it; a black popular culture site refused to review it. A blogger for the Seattle alternative paper, the Stranger, has called for the studio to “pull the plug” on the movie altogether.

The twist: Parker was actually tried, and acquitted, on the rape charge 15 years ago.

For many, it seems, an accusation of rape now equals guilt not only before there is a conviction but even after a not-guilty verdict. This may look just to those for whom “believe the survivors” is an article of faith. But such “justice” will inevitably shatter lives — and may hurt victim advocacy by lending credence to fears that rape accusations are a danger to the innocent.

In Parker’s case, the circumstances are especially murky, and the charges especially difficult to prove or disprove. The alleged victim, who had previously had consensual sex with Parker, had been drinking with him and his friend Jean Celestin at another friend’s apartment before going to Parker’s place. The young woman testified that she had only disjointed memories of being raped by both men while drifting in and out of consciousness. Parker and Celestin claimed that she willingly had sex with them both. Witnesses who had seen the woman that evening or talked to her on the phone gave conflicting accounts about her intoxication level. Parker’s roommate testified that he walked into the room to see Parker having intercourse with the woman, and she did not appear to be moving; however, there was some evidence that his testimony had been coerced under threat of prosecution.

Parker was acquitted on all counts. Celestin — Parker’s co-writer on “The Birth of a Nation” — was convicted of sexual assault and served time in jail, but his conviction was later overturned on the grounds of inadequate legal representation, and prosecutors chose not to retry him.

Writing in the Hollywood Reporter, Amy Ziering, producer of “The Hunting Ground,” the acclaimed but much-debated documentary on campus rape, makes it clear that she believes the probability of Parker’s guilt is overwhelming — even though she has no direct knowledge of the case. (“The Hunting Ground” has been criticized for its treatment of two rape cases in which the defendants were exonerated; critics say the film skews the facts and wrongly assumes the men to be guilty.) One of Ziering’s arguments is that “92 to 98 percent of the time, when someone reports a rape they are telling the truth.” Gay echoes this claim, stating that “2 to 10 percent of rape accusations are false.”

But in fact, estimates of false allegations vary widely. A 2010 study by psychologist David Lisak found that 6.8 percent of sexual assault reports on a Northeastern university campus over a 10-year period were false. However, that statistic refers only to cases in which there was actual evidence disproving the complainant’s story. More than half of the reports in Lisak’s sample were investigated and closed with no criminal charges, usually because of insufficient evidence or because the complainant stopped cooperating; it is impossible to tell how many were true or false.

Besides, the line between “true” and “false” is not always clear, particularly when it’s a question of consensual drunk sex vs. incapacitated rape. An encounter seen as disappointing or degrading, and remembered through an alcoholic haze, can be sincerely reinterpreted as rape later on — particularly given the elastic and often subjective definitions of rape that have been used in college sexual assault prevention programs since the 1990s.

Did Parker force himself on an unconscious woman? Was the charge against him a product of confusion and regret? The truth remains elusive. But the rush to judgment has been swift and ruthless, despite the fraught racial politics of the case: Parker and Celestin were black men accused of raping a white woman and tried before a nearly all-white jury — with the exception of a lone African American woman — in a conservative Pennsylvania county. That jury acquitted Parker.

In the past two or three years, amid the heightened awareness of sexual assault that some have called a moral panic — and partly as a reaction to real and perceived inadequacies in the legal system’s handling of rape complaints — a number of accused men have faced trial by Internet and the media. In some cases, most notably Bill Cosby’s downfall, there has been solid journalistic work to investigate the charges, and the result was almost certainly an overdue correction of an injustice. Yet in other instances, accusations have been embraced with little critical scrutiny.

Literary magazine editor Stephen Tully Dierks left public life after young Canadian writer Sophia Katz accused him of pressuring her into unwanted sex and another writer backed her and labeled Dierks a rapist — even though his actions as described by Katz almost certainly would not meet the legal definition of rape. Max Temkin, co-creator of the game Cards Against Humanity, was vilified online and dropped from at least one cultural event after a former college friend claimed he raped her. (According to Temkin, they had a brief relationship that he ended in an insensitive way.) Columbia University student Paul Nungesser became a campus pariah when fellow student Emma Sulkowicz claimed he brutally raped her during an encounter that started out as consensual, even though he was exonerated by a university panel under a much lower standard of proof than in the legal system.

And just last week, Kurt Metzger, a former writer for the comedy show “Inside Amy Schumer,” faced an online firestorm over a Facebook post that skewered the trend of informally “convicting” men of rape without evidence, police reports, or detailed charges. (The occasion was a comedy club’s banning of a comedian accused of “nonconsensual sex” with a woman too intoxicated to give consent and of several other unspecified sexual assaults.) Metzger’s sarcastic comments were crude and deliberately inflammatory — but he had a point.

Granted, the presumption of innocence and the burden of proof are concepts that apply to the criminal justice system. There is no constitutional right to film reviews or a comedy club gig. Nonetheless, it has long been understood that justice also requires a cultural climate in which the accused are given the benefit of the doubt. Someone who commits a crime in broad daylight in front of a scores of witnesses is still “the alleged perpetrator” until convicted — and someone who is found not guilty is treated as innocent, barring a glaring miscarriage of justice.

When support for the presumption of innocence weakens in the culture, the courts will inevitably be affected, too. Last month in Canada, a judge in a non-jury case involving two graduate students, he said/she said accounts of coercion and consent, and alcohol-addled recollection arrived at a guilty verdict by choosing to accept the woman’s testimony as fact and disregard the man’s.

We are rightly wary of the misogynist subtext in the cliche of the woman “crying rape.” But it is equally sexist to put women who come forward as rape victims on a pedestal of absolute credibility — and this form of chivalrous sexism, too, is a very real and ugly part of our history.

As we seek to do right by victims of sexual violence, cases in which the alleged victim and the alleged offender each tell a plausible story pose a vexing dilemma. Let’s not try to resolve it by discarding fundamental principles of justice that protect everyone. And let’s not make Nate Parker the scapegoat.