Piling onto the California rape conviction of Harvey Weinstein, losing Manhattan DA candidate Tali Farhadian Weinstein and Jane Manning, former prosecutor and Women’s Equal Justice Project argue in the New York Times that propensity evidence should be admissible in court, but only for sex crimes.

Disagreements over how much a jury should know about a defendant aren’t new. The American legal system has long checked prosecutors’ wish to share negative history about the accused. Prosecutors pursue crimes, not people, and we are supposed to hold people accountable for their bad acts, not their bad reputation.

As such, courts rarely allow prosecutors to present evidence of the defendant’s “prior bad acts.” There are exceptions — for example, if that evidence helps to establish a motive, or to undermine a claim that something happened by accident. Even then, courts must decide beforehand that this evidence is important enough to outweigh any prejudicial effect it might have on the jury.

Under the federal rules of criminal procedure, this is covered by Rule 404(b),

(1) Prohibited Uses. Evidence of any other crime, wrong, or act is not admissible to prove a person’s character in order to show that on a particular occasion the person acted in accordance with the character.

(2) Permitted Uses. This evidence may be admissible for another purpose, such as proving motive, opportunity, intent, preparation, plan, knowledge, identity, absence of mistake, or lack of accident.

Under New York law, this is set forth in a 1901 decision, People v. Molineux. These are rules, and exceptions, of general applicability, subject to the general rule (403 in the federal rules) that evidence must be more probative than prejudicial.

The problem with prior bad act evidence is that its purpose is to show that a defendant has a propensity to commit the crime, meaning that a jury might convict a defendant not because the crime before them has been proven beyond a reasonable doubt, but because he’s a bad dude who does bad things, particularly the bad thing with which he’s charged here. And if he didn’t do it this time, so what? He’s a bad dude.

Notably, California has a statutory exception for sex crimes, and only sex crimes, when it comes to introducing evidence of prior bad acts, because it’s California and sex crimes are special. The feds do too, although it’s rarely used since sex crimes are almost always prosecuted by states.

To us, that makes sense. Sex crimes differ from other crimes both in how they happen and in what it takes to prove them. Often, you don’t have witnesses to a crime committed behind closed doors, and sometimes in the context of an intimate relationship. But what you may have are other victims, who can echo and corroborate a victim’s account of violence. This is critical because, even today, jurors come to court steeped in sexist biases — for example, that “real” rape victims fight back physically against their attackers and report sex crimes immediately. These cultural prejudices cast doubt on the individual accuser. A group of accusers is harder to dismiss.

While the word “propensity” appears nowhere in their op-ed, that’s exactly the point, that it can be hard to convict for a sex crime because the evidence is lacking or equivocal, so the only way to assure the conviction is to make sure the jury knows the defendant has a propensity to commit the crime and let that become a substitute for evidence that he committed the crime with which he’s charged.

For those who are — rightly — concerned about defendants’ rights in these trials, California law has guardrails. Judges must decide whether the value of presenting “prior bad acts” to the jury outweighs their potential to influence the jury unfairly. Jurors are instructed first to decide whether the alleged similar crimes actually happened, and only then to consider whether that makes it more likely that the charged crime did. They are cautioned that similar crimes are “only one factor to consider along with all the other evidence” and that they may only support, rather than substitute for, evidence of guilt of the charged crime. California law trusts jurors to follow these rules.

In other words, believe with some unmentioned burden of proof that the defendant committed crimes with which he wasn’t convicted, and then bootstrap those crimes to satisfy a preponderance of the evidence (more likely than not) belief that if he did those, he did this. Because propensity.

The central insight of the #MeToo movement has been described as “the power of numbers across time” — in other words, the strength of a chain connecting one victim’s experience to another’s. That does not mean that every allegation of a sex crime is true, or that every defendant is guilty. Survivors’ accounts must be tested and considered critically, like any other evidence. But when a chorus of women, like those who testified against Mr. Weinstein, stands ready to describe violence that occurs in private and too often is disbelieved, that chorus must be heard, both in everyday life and in the law.

At the moment, there are 16 states plus the federal government who make special exceptions for sex crimes (not murder, mind you, but sex crimes). A bill has been introduced to do the same in New York. Should propensity evidence be admissible? Should it be admissible only in sex crimes? Should defendants be convicted because they are proven guilty beyond a reasonable doubt, or because the “chorus must be heard”?

*Tuesday talk rules apply.