On a side note, for those who want a "progressive" tax system I can demonstrate how a flat tax is a "progressive" tax ...
Now, supposing that the average household income level is $100,000 and the average services provided by the government cost and are worth 20,000 per household (for easy calculation) and every household uses an equal portion of government services. With a flat tax system an household making $1,000,000 would end up paing $200,000 (or ten times the cost of services they received) while a household earning $40,000 would only pay $8,000 (or 40% the cost of the services they received).
In most countries it is even more "progressive" being that the lower the income a person earns the greater the value of the services they receive from the government. Suppose that the average household income and average value of the service remains the same as above, but the household making $1,000,000 only receives $10,000 in government services while the household earning $40,000 receives $24,000 in government services. What this means is that the "Rich" household ends up paying 20 times the value in services they receive while the "Poor" household pays 33% the value of services.
To convert this into another context ...
Two old friends go out to eat a mean and the wealthy friend (who is whatching their weight) orders a light salad and takes it easy on the drinks while the poorer friend eats a more expensive meal. The total bill comes to $100 with the poor person's portion having cost $60 with the rich person's portion costing $40. Since the rich person earns 9 times as much as the poor person a flat tax system would suggest that the rich person should pay $90 while the poor person would pay $10. In a classical "progressive" tax system the rich person would pay $120 while the poor person would pocket $20.