Here's The Moral Basis For Progressive Taxation

[whatthehey]

13. I suspect he, and I know I, assume it is axiomatic

People have basic needs, and auxilliary wants. People can quibble with minutiae of Maslow but his basic thrust is universally acknowledged. The less you can afford, the greater percentage of what you have is chasing the lower stages of the hierarchy, so taxing you at an equal rate to those whose needs are well and truly satisfied along with an ever-increasing amount of wants as income increases, is increasing a greater harm to a greater number. A just civilization will tax more where the reduction in disposible dollars taxation causes harms the least number to the least extent. In short, taxing a person who cannot afford decent shelter and food the same as a person who might simply have to settle for a silver-plated Bugatti instead of gold when taxed is not really up for debate ethically speaking is it?

If utilitarianism doesn't seal the deal, there's the Willie Sutton answer too.