Which is a position completely ignorant of the marginal utility of money. No, it isn't fair that for one guy 10% could be the difference between getting by and not getting by while for the other guy 10% means no change to his lifestyle all.
No, progressives think it's fair that the burden is felt equally and that requires understanding how money works.
> 'Fair' depends strongly upon one's beliefs, and can't be objectively defined.
Fair does depend on beliefs, but some people's beliefs are objectively stupid. Anyone who denies the marginal utility of money and insists a flat percentage is fair, doesn't understand money and doesn't belong in the conversation just as anyone who believes vaccines cause autism is objective stupid and doesn't belong in that conversation. Everyone has opinions, that doesn't make them equal.