Blacks support high taxes and big government in larger percentages than whites because higher percentages of them do not pay taxes. That is the biggest argument for a flat tax that has a rate that does not alter for different income levels and for an end to Entitlements. It’s all free to those people and they do not see the future any better than most of everyone else.
Your first sentence is true, but a flat tax entails a sales tax, sometimes given the slightly different-in-meaning euphemism “value-added tax,” which hurts low-income people more than high-income people, so many black people would be very foolish to be in favor of a flat tax.