Um... The discussion was about a flat tax. We have no idea what the equilibrium point for that might be, especially for a national tax. It’s much harder to move to a new country or work off the grid than it is to move to another state. Since the rate would have to be between 17% and 20% to fund the current rate of spending, the results would be interesting. It’s been quite some time since I took micro or macroeconomics. Do you suppose the point would be called the coefficient of elasticity?
Do your own research. Look at Govt revenues over time. It is pretty steady when marginal rates are high. When marginal rates are lowered, like in the 80’s, revenue increases dramatically. Like I said just look at federal income revenue vs. tax rates. The data is readily available.