While reading through the economic policy proposals by Mike Huckabee, I came across the statement that a flat tax, unlike a progressive income tax, would not punish people for working hard. At first sight, but only upon first sight, does that seem plausiable. There are good reasons why the vast majority economists endorse a progressive income tax structure and would disagree with Mr. Huckabee's take on social justice and taxation. Here are three (note that there are more reasons, some of which may well be more compelling than those below) why the assertion that a progressive income tax punishes people for working hard is misleading and, quite frankly, nonsensical:

1. Hard work and material prosperity do not always go hand in hand. Even the prominent libertarian Friedrich van Hayek realized that the distribution of rewards in capitalism is not always just. Thus, we need to consider that the rich are not rich merely because they work harder; many do work hard, but coincidences - meeting the right people at the right time - as well as connections and inherited privilege play a huge role.
2. Even assuming, for simplicity's sake, that hard work always translates into increased material well-being, progressive taxation does not punish those who work hard. All it does, is distribute the tax burden equally, where everyone gets hit as hard as everyone else with the cost of maintaining society. Under progressive taxation, the marginal gains made by a hard working person who accumulates considerable material wealth do not diminish. He or she gets hit as hard with the cost of maintaining society as a working class or poor person.
3. But doesn't a flat tax and not a progressive tax structure distribute the burden equally? No. Suppose you have two people: John who makes $35,000 and Jody who makes $800,000 per year. Suppose we institute a flat tax of 20%. John will pay $7,000 and Jody $160,000 in taxes. Afterwards, John is left with $28,000 and Jody with $640,000. Now the question who was hit harder, $7,000 is a large sum of money for John, whereas Jody is still left with a large, large net income, even after paying $160,000 in taxes. True, both paid the same percentage, but John was hit much, much harder by the tax than Jody. Paying 20% of his income in taxes is mighty painful for John, but not for Jody, because her income is so much higher.

The above is of course a simplified and condensed argument, but I think it gives an idea of why progressive taxation and not a flat tax is the truly just way to distribute the burden of society. After all, even Adam Smith himself stated that "The rich should contribute to the public expense, not only in proportion to their revenue, but something more in proportion."