Dick Armey, proposed a flat tax during the Clinton administration .. that's about enough to negate the idea for me
"Critics of the flat tax argue that the marginal dollar to the low income is vastly more vital than that of the high income earner, especially around the poverty level. In their view this justifies a progressive taxation system as the added income gained from a flat tax rate to the rich would not be spent on vital goods and services for survival as they might at the poverty level with reduced taxation. However, true Flat tax proponents necessarily contest the concept of the diminishing marginal utility of money and that a marginal dollar should be taxed differently. ..