Indian Finance Minister Arun Jaitley says “India has to move towards the cashless society.” Cashless society? India? Last month’s demonetization continues to wreak economic havoc, and now defenders say it will pay off long-term by promoting digital-payment systems that increase efficiency and transparency. But why should Indians believe that officials exercising arbitrary power over their cash will keep their hands off a system that monitors every transaction?

In a cashless society the state has far greater means to harm the...