OK, just talking fed income tax, the fairness of any system, including a flat tax, is predicated on how it is setup. If you allow deductions (for homes, kids, investment losses/gains, manipulations, etc) then they will be abused. Any way given to turn real income into AGI (adjusted gross income) can be leveraged so that those with the resources can hide/defer income. For example, if joe the plumber pays 15% of his actual income of $30K ($4500) and Richie Rich pays 15% of some fraction of his income that is not fair. Richie Rich accomplishes this by saying that his yacht is a tax exempt business expense, or that his flights across country to nail his mistress are business related. So his $1mil yearly income, which he should pay $150K in taxes on, becomes $600K and he pays $90K instead. So in comparison, Joe the plumber paid 15% of his income in taxes, but Richie Rich paid 9%.