I can remember when people actually advocated for a flat tax with a straight face. Freaking hilarious idea supported by shallow thinkers.

It wouldn't surprise me, though I've usually seen that applied as a reductio ad absurdum to show that the notion of a flat percentage as "fair" is arbitrary because surely a flat tax would be even fairer - on the basis that it highlights how flattening out the tax curve can make the burden on the poorest unsustainable.