Four years ago Mr. Brown’s career as a boy-next-door pop star seemed to come to a sudden end when he was charged in the brutal beating of Rihanna. Excoriated by every sector of the media, he pleaded guilty to felony assault and was given five years of probation.

But now Rihanna, 25, has publicly embraced the boyfriend who once abused her, creating perhaps the most polarizing spectacle in pop culture. To their fans, the couple represent a story of forgiveness and happy endings. To a ravenous celebrity news media, their every affectionate tweet or late-night indiscretion is reliable hot copy. And to many others, Rihanna’s decision has inspired fear and worry about the example she is setting in what has become the signal domestic abuse case of the social media age.

Laurel Eisner, the executive director of Sanctuary for Families, a group in New York that serves domestic violence victims, criticized Rihanna’s decision to return to Mr. Brown — and gossip outlets that cheer it on — as a “fantasy message to young girls” that conflicts with reality.

“A magazine that sends out the message that it is O.K. is taking a risk with girls’ lives,” she said. “There is almost nothing to support the notion that a man who is as impulsive and as close to anger as he is, and who continues to repeat misogynist messages — there isn’t any evidence that men like that will change.”