There are two basic sources of income in this country:
1) Pay for what you do. and
2) Return on what you own.
Now, the tax code is full of exemptions and lower rates for income on what you own. Each argument is particular, but the general idea is that if what people own is, or could possibly be, of some general benefit, then it shouldn't pay the same tax rate as nurses and firemen pay on their income for what they do.
I'd suggest that the egalitarian position is the reverse of that. All returns on what people own should be taxed. If the economy can afford it, the first $X of the income from what people do should not. The value represented by X should be determined by the state of the economy.
Such a restructuring of the income-tax system would generate a lot of resistance, but the results would be worth it. It seems to me that attempts at slight restructuring already generate loads of resistance, and they wouldn't really solve the income problems of the federal government.