Income tax is far from the only tax we pay. Don't forget FICA, sales tax, fuel/utilities tax, phone tax, airline tax, etc. If I buy a gallon of gas, I pay tax on it. If I buy groceries, I (usually) pay sales tax (varies by state). If I have utilities or a phone in my name, I pay taxes on it (check the bill!). If I buy a car, I pay tax. And a millionaire pays the same tax on a $25K car as a poor person.
And don't forget property taxes! Of course, that is often tied to the value of your home (more value, higher taxes). But property taxes are deductable IF YOU ITEMIZE. In Texas, the median HOUSEHOLD taxable income is $30K. Only 5% of people who make $30K and under itemize their taxes in Texas, so they don't/can't take advantage of that "tax deduction". (Overall itemization is closer to 25% state-wide, meaning that 80% of people who itemize are in the "wealthy" half of households). I'm one of the people who can't: the standard deduction is higher than all of my itemized deductions (which includes my property taxes, sales taxes, etc). Renters (who are usually poorer than owners) pay for property taxes indirectly through higher rent.
Yes, the more you buy, the more you pay. But MORE of your income is taxed, proportionally, when you purchase and/or use consumer goods. That's why I (and many "rich") do not like the flat tax system. It hurts the poor. Remember Bush and his "awesome" tax cut? Part of it was to cut the capital gains tax down to 15% (which is the lowest tax bracket). How many "poor" actually earn capital gains versus "rich"? In addition, the rich are more likely to itemize (since they are more likely to own a home (mortgage interest, property taxes, etc) and have other deductable "expenses"), so they have LESS taxed income. For example, my aunt/uncle pull in at least a half-mil per year, but they pay less in income taxes, in overall dollars, than my parents (who make maybe $80K/yr) because of many tax sheltered accounts, etc.
Does that answer your question?