A number of conservative politicians and economists advocate replacing the progressive income tax with a flat tax

Question:

A number of conservative politicians and economists advocate replacing the progressive income tax with a "flat tax" that would apply the same, low tax rate to all income above a certain exempt amount. One argument against making this change is that the of income has grown much more unequal since the 1970s. Does the evidence support that view? Is it a decisive argument against a flat tax? How is the trade-off between equality and efficiency involved here?
Distribution
The word "distribution" has several meanings in the financial world, most of them pertaining to the payment of assets from a fund, account, or individual security to an investor or beneficiary. Retirement account distributions are among the most...