I'll go you one better, Mr. G. We tax ALL income, earned and investment. No deductions period.

Exempt from taxes a basic, no frills living standard.

Set the tax rate at a reasonable percentage for everybody above that rate.

For example:

Exempted Income, $25,000
Assume tax rate beginning at $25,001 of 12.5%

Earnings                Tax          Effec Tax Rate
   30,000                625.             2.01%
   50,000               3125.             6.25
125,000             12500.            10.00
500,000             62500.            11.90
1,500,000             184375.            12.30

You can see as income gets higher, the effective tax rate becomes asymtotic to the actual tax rate of 12.5%. It satisfies the concept of the rich paying at a higher effective rate than a poorer person, and everyone who makes more than the exempted minimum pays a fair share.

Of course the rate could be 10% or 15%, or any reasonable rate, and the exemption could be a bit higher or lower.

Then we'd have to decide if a married couple would be required to file jointly or if they could file separately. Would a couple each making $20K be allowed to file separately and pay no taxes, or be required to combine household income and pay taxes on 15K of their combined 40,000 income?

I think some form closely resembling this program is eminently fair. Only a CPA or an IRS person would hate this type of taxation, because everybody who can do basic arithmetic, would be able to prepare their own taxes.