I am not all that interested in a progressive income tax.
For one thing “income” is very easy for the rich to hide. For example, money earned as stock options may never be taxed until they are exercised but it can be used to take loans at low rates .. and the interest on those rates is tax deductible. Same is true for income earned by any increase in the value of an asset and even that is often written off by “depreciation.”
A different approach is to tax non-productive wealth.
If you are rich and “invest” in mansions, yachts, baubles, and brocades, fine but that wealth should be taxed. Same for wealth invested in foundations, churches, art, art museums. Foundations are a GREAT wealth gimmick because money placed in a foundation is not taxed but control of that money remains in the “investor’s” hands. Then there is the question of wealth invested in China or worse Bermuda and Ireland or Monaco or Swiss Banks.
Why should the American taxpayer subsidize wealth that does not build the American economy?