A Flat tax could be designed to be simple, fair, and workable. It could also be made tamperproof.
Allow only one deduction with no exceptions, earnings up to the federal poverty level, everything above that amount would be taxed at the determined flat-tax rate.
The federal poverty level deduction could only increase/decrease with the rate of inflation/deflation.
The Flat-tax rate would include a percentage to be used for social security/Medicare.
It would be written right into the law that any change to the Flat-tax rate would require a vote of 2/3 of both houses of congress, and any change to the one and only deduction ( earnings up to poverty level) would void the entire law.
Married, single, 10 kids or none at all, only that one deduction that everyone would get.
Wages, capital gains, earnings on interest/bonds, whatever, all the same Flat tax rate.
Congress has the power to make, change and amend laws. You can’t make anything “tamperproof” from Congress unless you pass a constitutional amendment. But then whatever constitutional tax amendment you would pass would then conflict with the 16th amendment.
So you’re screwed.
This is why:
A FLAT TAX NEVER STAYS FLAT!
A flat tax is not fair, why should I have to pay more than someone else?