The Minnesota Court of Appeals on Tuesday struck down Minnesota’s defamation law, ruling in the case of a man who published sexually explicit ads on Craigslist after he had a fight with his girlfriend.

The Court of Appeals ruled that Timothy Turner, of Isanti County, had a First Amendment right to post the messages, which resulted in his girlfriend getting phone calls from men seeking to have sex with her.

In her ruling (pdf), Judge Denise Reilly wrote that the defamation law under which Turner was convicted is “overbroad.”

The case drew the attention of legal blogger and professor Eugene Volokh, who submitted a brief on Turner’s behalf. He argued that even true statements can be prosecuted under the Minnesota law, something Reilly said “chills” free speech.

Here’s part of Volokh’s argument submitted to the Court of Appeals:

For instance, after breaking up with a cheating boyfriend, a woman may naturally want to talk to her friends and family about what happened, or inform her Facebook “friends.” Yet under Minn. Stat. 609.765 she could be criminally convicted if the jury decided she had bad motives (perhaps such as revenge or a desire to humiliate the ex-boyfriend) rather than good motives (such as a desire to warn her friends about the ex-boyfriend’s tendencies or to explain her conduct to her loved ones). Likewise, a person who had a poor experience at a local restaurant would naturally tell his friends and give the restaurant a bad review — but this review could expose him to criminal liability if a jury was not satisfied with his motive.[2] People may thus become hesitant to criticize others (especially when those others are known to have the ear of the local prosecutor) for fear of a prosecution. Even when they know their own motives are pure, they may worry that the prosecutor and a jury might wrongly conclude otherwise. And this is especially so given the established Minnesota criminal defamation precedent that, “[a]fter the production of proof showing the publication of the libel, the burden [is] upon the defendant to establish such justification, or to show that, in excuse of the same, it was published upon reasonable grounds of belief, and from good motives.” State v. Shippman, 86 N.W. 431, 445 (Minn. 1901) (emphasis added); see also State v. Hage, 595 N.W.2d 200, 206, 207 (Minn. 1999) (concluding that criminal statutes may require justifications to be proven by the defendant by a preponderance of the evidence, so long as the justification does not “disprove or negate any element of the crimes with which [the defendant] was charged”). This chilling effect is exacerbated by the difficulty of determining motive, and the uncertainty about what motives are good. Is the desire to expose a cheating ex-boyfriend to social ostracism a good motive (on the theory that it will deter other such behavior in one’s social circle) or a bad motive (on the theory that it is simply the desire to harm)? What about the desire to expose a woman’s alleged promiscuity? It is hard to predict how a jury would evaluate such motivations, especially given the lack of Minnesota caselaw on what constitutes bad motive. Moreover, people often have multiple motives for what they say. For instance, people may post negative restaurant reviews both because they want to warn others about what they see a terrible restaurant, and because they personally dislike the restaurant owner. Indeed, human nature being what it is, one motivation is likely to help produce the other; we are more likely to be unhappy with our experience at a business if we dislike its owner, and vice versa. And it is unclear from the statute whether the “good motives” defense is satisfied when at least one of the speaker’s motives is good, only when all of the speaker’s motives are good, or when the good motive predominates (whatever that might mean).

None of this excuses Turner’s behavior. It was “reprehensible and defamatory,” Reilly wrote.

But his conviction was unconstitutional, she said.

Turner’s case prompted a Minnesota legislator to file a bill in the recent session making it a felony to impersonate another person — Turner pretended to be his girlfriend — on social media.