Mitt Romney and his fellow conservatives claim that 47% of Americans don't pay taxes. The graph below tells another story. It shows the total taxes paid as a percent of income. The tax system is slightly progressive. The highest income group pays 1% more of their income in taxes than the national average. That is because the income tax system is progressive and they earn more of the income. They pay a smaller share of social security taxes because no taxes are collected on income over $108,000, and only wage income is taxed. There is no Social Security tax on capital gains, interest income or dividends. Social Security revenues are around the same as those collected through the income tax. All wage earners pay the 15.6% social security tax.
The GOP gets away with their claims about taxes because most Americans no very little about the tax system. You can have a interesting conversation with your conservative friends by showing them the breakdown on taxes provided in this link.