Can malicious speech constitute violence? No. But Friday’s shocking court decision — which found Michelle Carter guilty of sending lethal text messages — is bound to confuse the issue.

Judge Lawrence Moniz, of Bristol County Juvenile Court in southeastern Massachusetts, ruled that Ms. Carter, 17 at the time of her crime, had committed involuntary manslaughter by urging her depressed 18-year-old boyfriend, Conrad Roy III, to kill himself. Mr. Roy had flirted with the idea for weeks, and Ms. Carter — after initially telling him to seek counseling — seemed to warm to the idea, consistently egging him on via text: “The time is right and you’re ready, you just need to do it! You can’t keep living this way. You just need to do it like you did last time and not think about it and just do it babe.”

On July 12, 2014, Mr. Roy drove to a Kmart parking lot and connected his truck to a water pump that released carbon monoxide. At one point, sick from the fumes, he got out of the truck. Ms. Carter told him to “get back in.” His body was found on July 13.

Ms. Carter also struggled with mental illness. Her lawyers claimed antidepressant drugs influenced her behavior; though the prosecution preferred to cast her as a callous narcissist who craved the sympathy of her peers and believed a suicidal boyfriend would earn her a popularity boost.