Flat tax wouldn't solve the fundamental problem, which is making people calculate their own taxes. In the vast majority of countries with personal income tax,

Flat tax wouldn't solve the fundamental problem, which is making people calculate their own taxes. In the vast majority of countries with personal income tax, everything is automatic and individuals don't need to do anything. Political parties in the US have an incentive to make things as complicated as possible to trick people into thinking ideas like a flat tax would be helpful.