A flat tax is a poor tax. 5% of your income means WAAAAY more to someone working minimum wage with two kids than someone who has a second home, even if dollars and cents it's way less. And the wealthy will evade a flat tax as much as they already do a progressive tax.

Now, if it was a flat tax, a fixed percent…But they gotta make sure the middle class is paying 22% of their income to the feds and the billionaires pay one tenth of a percent… you know… for reasons.

I fall into the lower end of the middle class (nationally) and my income tax is about 11%, but on top of that, after deductions and credits I end up deducting myself into the lowest tax bracket and collecting credits so I get a nice chunk back every year. To actually pay a full 22% of your income in income taxes, you must be making pretty good bank (and probably spending pretty good bank if you're still considering yourself middle class)

Flat taxes are extremely regressive. The whole idea of tax brackets is that those with more ability to pay pay more and those with less ability to pay pay less. If you only make 22k/year you need all of that and that $2200 can be pretty lifechanging, but if you make 220k per year you can live without that $22k. There's also fun stuff with how much tax revenue the government can actually bring in depending on who they tax harder, and generally it favors taxing the rich at a much higher percentage rate than they do the poor.