“We are a society that won’t mobilize very much, won’t act against deadly violence,” she said.

As the sense of collective good recedes, neglect is becoming the new norm.

“In some slums of the city, there is no presence of the state,” she said. “There is nothing, literally nothing. Young people have to take care of each other in the street.”

Mr. Salas, the Juárez robbery victim, expressed optimism that the social contract could be repaired if communities unlearned their new habits.

“It is a cultural thing that was put together little by little, so you have to dismantle it and then put it back together piece by piece,” he said. “I bet on that. That’s the reason I’m not moving.”

But Ms. Treviño, after watching years of work on poverty and governance unravel, worries that society might not come back together again.

“It’s very serious,” she said.

“As I say this, it’s making me emotional,” she added, tears of frustration rising in her eyes. “It’s overwhelming.”