A new study from the Adam Smith Institute in the United Kingdom provides overwhelming evidence that class-warfare tax policy is grossly misguided and self-destructive. The authors examine the likely impact of the 10-percentage point increase in the top income tax rate, which was imposed as an election-year stunt by former Gordon Brown and then kept in place by his feckless successor, David Cameron. They find that boosting the top tax rate to 50 percent will slow economic performance. And because of both macroeconomic and microeconomic responses, tax revenues over the next 10 years are likely to drop by the equivalent...