Tales of official malfeasance abound, the rich drive Lamborghinis without license plates and good Samaritans appear to be in short supply. Lei Feng’s good deeds sound especially hollow to Chinese still shocked by the inaction of the two dozen people who last year walked past a mortally injured 2-year-old as she lay in the street after being run over by two vehicles.

Li Chengpeng, a sports writer and novelist who commands a huge Weibo following, said that government-sponsored role models strained credulity. Previous party icons include Iron Man Wang, who dog-paddled in a vat of cement when there was no machine to mix it; Shi Chuanxiang, a happy-go-lucky “night soil” collector; and Wang Yiqing, an electronics worker who assembled five million radio parts without a single mistake.

“China has had hundreds of these somewhat fake role models,” Mr. Li said in a phone interview. “They don’t work because they don’t represent the right values. Lei Feng is a good guy but he doesn’t have critical thinking skills, doesn’t reflect on things and only follows marching orders.”

Western scholars have long questioned the Lei Feng biography, and now the Internet has given rise to deniers who have been merrily poking holes in his story. They have questioned how a poor orphan living on a tiny army stipend could donate so much money to the needy, and how he collected more than 300 pounds of cow dung on a single day during Chinese New Year.

Others have questioned the flawless script in his official diary and wondered how there came to be hundreds of photographs recording his every good deed. Liu Yi, a designer in Shanghai, pointed out the absurdity of one famous image showing Lei Feng in bed reading Mao’s collected works by flashlight — except that the flashlight is off and the room is fully illuminated. “And there just happened to be a photojournalist passing by to capture the moment,” he wrote.

If the maelstrom of ridicule seems particularly intense this year, it might be because Weibo users — whose numbers recently surpassed 300 million — realize the days of unfettered, anonymous criticism may be drawing to a close. Beginning on March 16, new government regulations will require real-name registration. Another rule will require Sina Weibo to review the posts of those who have more than 100,000 followers. Those “harmful” to national interests, according to the rules, must be summarily deleted within five minutes.