That’s progressive taxes. Consider that roughly the bottom 60% of Americans have no federal income tax liability, simply because they do not make enough. That 60% cannot meet their basic needs on their incomes, very roughly speaking. Any increase of taxes on them would be regressive.
Indeed. I should rephrase that I think it would be feasible to use propaganda/marketing to redefine what a "flat tax" is, and make the most popular definition one where the basic living wage is exempt and the "flat tax" only applies to the amount over that.
Through that confusion of language, it might then manage to be popular with both libertarians and progressives.