Proportionate taxation always is what progressive taxation never is: simple. What justifies progressive taxation, and characterizes progressivism, is confidence that at any moment in society’s endless evolution, what is equitable can be known and society can be fine-tuned to achieve it. Which is how we got our baroque tax code.

As Blum and Kalven noted, “It is the very nature of majority rule that the majority can vote distinctive burdens for the minority.” It is, however, the nature of reality that burdens imposed on the wealthy minority can injure the majority by impairing economic incentives, thereby suppressing growth. Progressive taxation reduces the rewards of investments and the real rate of return on savings, thereby encouraging consumption over saving and hence over capital formation. When progressive taxation slows economic growth, it makes inequalities of wealth more durable by retarding the accumulation of new fortunes. And by encouraging constant tinkering with the tax code to perfect equity, progressive taxation gives a patina of altruism to rent-seeking by economic factions, whereby government enriches those sophisticated at manipulating it.

Because other arguments produce only “uneasy” cases for progressive taxation, this is the argument of last resort: All striving occurs in, and all success is conditioned by, a social context.