There is something intoxicatingly utopian about the story of Tancítaro.

This small town has succeeded at self-rule in a part of Mexico — the state of Michoacán, drug war ground zero — where so many similar experiments have failed. It is free of the drug cartels as well as the Mexican police and politicians who are widely seen as part of the problem. It has homegrown institutions. It is safe.

“It’s a nice town. You can walk around at day or night. It’s very nice,” Guillermo Valdés, a former head of Mexico’s national intelligence agency, told us this August. “They take care of themselves.”

Mr. Valdés told us about Tancítaro at the end of a long interview at a Mexico City cafe, where we had met him to discuss towns that were seceding in subtler ways. It was the sort of comment sometimes made after the formal questions have ended and the notebooks have closed, the casual aside that changes the whole story.

He’d recently visited Tancítaro for a book he was writing on the drug war and found its experiment in self-rule intriguing. It’s a global center in avocado production, exporting about $1 million worth every day. The orchard owners use that money to fund militias that guard and police the town.