Recently a video went viral of a plain clothes Hong Kong police officer aboard a minibus counting how many passengers had not fastened their seat belts. The police said summons would be issued to commuters who had been found to be not wearing seat belts. Social media lit up with surprise, amusement and debate. Some wondered if undercover policing could soon spread to buses or taxis. The law itself is hardly new. Minibus passengers have been required to buckle up for more than 20 years. What...