Flat tax? Why not an "equal tax".
Not sure where we got this idea that taxes should be tied to income, uncless it's from the ol' Communist slogan, "From each according to..." I mean, why not peg taxes to AGE? It's just as irrelevant.
Why not take the total cost of government, divide it by the number of adult citizens, and send everyone a bill for the same amount? We all pay the same for a loaf of bread regardless of our income (or age), don't we? Your lawn service, dry cleaner, barber, babysitter, auto mechanic etc. charge everyone the same prices.
Why should government be any different?