It really depends on the metric you are using to measure fairness. Yes, a flat tax is fair on a purely dollar level, but it is completely unfair from utility st

It really depends on the metric you are using to measure fairness. Yes, a flat tax is fair on a purely dollar level, but it is completely unfair from utility standpoint in that the worse off suffer greater reductions in utility. The key thing to remember when thinking about the utility of money is that the utility of money is not linear. Going from $50,000 a year to $25,000 a year very significantly degrades your quality of life while going from $2,000,000 to $1,000,000 will have a much more minor impact. This is what causes the main issue with flat taxes. The problem is that at the end of the day, flat taxes are simply very inefficient in that they cause much more suffering for less revenue compared to progressive taxes.