When people on the opposing side say that the less money the wealthy members of society have, the more likely they are to "take it out on the poor" they are usually referring to large corporations rather than the people you see in the higher tax brackets. Sure, higher taxes does result in people feeling as if their effort is not worth it, but the simple fact of it is that even in those higher tax brackets the numbers are crunched in a way that they still make more than those in the lower brackets.
Less tax payroll employees equal to hiring employees that generate revenue. Working class don't drop $150 @tax franchisors to preparer a return that they could easily do themselves. Lump all normal expenses that IRS know people spend can turn into the new standard deduction. More time spent on revenue products, not piddling. "Simplicity simplicity simplicity" Thoreau
Flat taxation is the dangerous notion that if you reduce taxes on all income brackets, especially the rich's bracket, you will witness faster economic growth. This is false. Taxing (or not taxing) the rich has a negligible effect on affecting economic growth or productivity. This only applies to corporate taxes. Reducing corporate taxes has been shown to free resources and capital for better investments. Reducing taxes on the wealthy (primarily the super wealthy), however, stifles growth because it deters future public investment in infrastructure. Reducing taxes on the wealthy also means the government has less money to spend on equalizing opportunities (education) for the poor and middle class. The best method for improving growth is to drastically cut taxes on the middle class, remove taxes for the poor, and raise taxes on the rich. When the poor and middle class pay less taxes, this lowers their debt and provides additional income for consumption, which invariably increases demand for jobs.
Since a flat tax requires everyone to pay into the system, regardless of their income, it is less likely to help the poor. In a flat tax, everyone is made to pay the same percentage of their income, regardless of income. In progressive taxation we see different tax rates for different levels of income. This generally means that the poor pay little to no taxes, thus it helps them.
No, progressive taxation does not help the poor, because progressive taxes stunt the economy. If higher income earners cannot hire workers or grow their businesses because of taxes, that will hurt lower income people who will have to pay more for things or who might not be able to get a job. Also, lower-income people might not work as hard, knowing that if they earn more, their taxes will increase.