In last month’s deep and damning Rolling Stone report about sexual assault at the University of Virginia, a reporter told the story of “Jackie,” who said she was gang raped at a fraternity party and then essentially ignored by the administration. It helped dramatize what happens when the claims of victims are not taken seriously.

Now the narrative appears to be falling apart: Her rapist wasn’t in the frat that she says he was a member of; the house held no party on the night of the assault; and other details are wobbly. Many people (not least U-Va. administrators) will be tempted to see this as a reminder that officials, reporters and the general public should hear both sides of the story and collect all the evidence before coming to a conclusion in rape cases. This is what we mean in America when we say someone is “innocent until proven guilty.” After all, look what happened to the Duke lacrosse players.

In important ways, this is wrong. We should believe, as a matter of default, what an accuser says. Ultimately, the costs of wrongly disbelieving a survivor far outweigh the costs of calling someone a rapist. Even if Jackie fabricated her account, U-Va. should have taken her word for it during the period while they endeavored to prove or disprove the accusation. This is not a legal argument about what standards we should use in the courts; it’s a moral one, about what happens outside the legal system.

The accused would have a rough period. He might be suspended from his job; friends might defriend him on Facebook. In the case of Bill Cosby, we might have to stop watching his shows, consuming his books or buying tickets to his traveling stand-up routine. But false accusations are exceedingly rare, and errors can be undone by an investigation that clears the accused, especially if it is done quickly.

The cost of disbelieving women, on the other hand, is far steeper. It signals that that women don’t matter and that they are disposable — not only to frat boys and Bill Cosby, but to us. And they face a special set of problems in having their say.

“Rape culture,” as it is often called, is real. Because rape it is such a poisonous charge, we are so careful not to level it until we can really prove it. But this is exceedingly hard: The evidence vanishes quickly, often as soon as the survivor takes a shower; so unless she immediately reports the assault, much of the physical evidence is destroyed by the time she can get to a rape kit. (It doesn’t help that 400,000 untested rape kits are sitting on warehouse shelves collecting dust.) Many survivors do eventually come forward, but 60 percent of rapes are never reported to the police.

And while the clock is ticking on the physical evidence, survivors are often grappling with the first stages of post-traumatic stress disorder (PTSD), creating a perfect storm of foggy memories, isolation and denial. It’s common for them to experience a dissociative moment when they try to “get over it” and move on with their lives, says Andrea Pino, a survivor and co-founder of End Rape on Campus. “It wasn’t until 10 days after my rape, when finishing a half marathon, that I fully came to realize what had happened to me. I was covered in bruises, had lost my appetite, and even had been having nightmares, but I denied everything to myself; I couldn’t have been ‘raped,’” she says.

The lasting psychological wound left by sexual assault is unique — and makes justice less likely. Survivors’ memories are often blurry, and they tell conflicting stories about what happened to them. The narration Jackie gave to Rolling Stone, her friends, and a Washington Post reporter do not all agree with each other. This is not surprising given the research on the aftermath a sexual assault and how PTSD affects the hippocampus portion of the brain that controls memory. (No wonder only 3 percent of rapists go to prison.)

This is not because women lie. In fact (despite various popular myths), the FBI reports that only 2-8 percent of rape allegations turn out to be false, a number that is smaller than the number (10 percent) who lie about car theft. Yet while women claimed for years that Cosby had raped them, nothing happened. Instead, everyone who abetted and covered Cosby appeared to believe in “a massive conspiracy, between women who don’t know each other, all to bring down Cosby four decades after the fact and long after legal consequences are possible,” says Jaclyn Friedman, author of “Yes Means Yes!: Visions of Female Sexual Power and a World Without Rape.”

Disbelieving women, then, not only compounds their trauma (often by making them doubt their own stories), but it also lets a serial rapist go free. According to a 2002 study conducted by David Lisak at UMASS Boston, 90 percent of rapes on campus are committed by serial offenders who rape an average of six times. These people escape the rule of law — sometimes the perpetrator outlives the statute of limitations — and reinjure their victims.

The time we spend picking apart a traumatized survivor’s narration on the hunt for discrepancies is time that should be spent punishing serial rapists. “When a woman is coming forward to reveal that she has been sexually assaulted, statistics and empathy should demand we believe and support her. By loudly disbelieving Cosby’s accusers, no matter how unlikely it is that they are all lying, we are telling the survivors in our own lives, that we don’t believe them either,” says Friedman.

That means we have to admit that a rapist is not literally a monster; he is a person who chose to violate another person’s consent and bodily autonomy. Discrepancies in a survivor’s account are common, but we must be able to offer our hand of support to survivors without requiring them to have a video record of what happened to them as proof. We constantly wax poetic about how seriously we as a society take the dignity-crime of sexual assault, and yet we never seem to want to believe that anyone who has been accused is actually capable of committing it. Someone is out here raping 1 in 5 American women and yes, it could be someone that you know and love. It could be the boy at the frat party.

CLARIFICATION: The headline of this piece was changed shortly after publication. Due to an editing error, the author was described as a “lawyer” rather than a J.D. She has never claimed to be a practicing attorney.