Definition of "regressive tax": A tax that takes a higher percentage of income from low-income earners than from high-income earners.
By definition, the tax system in the post you replied to is not a regressive tax system.
By definition, the tax system in the post you replied to is not a regressive tax system.
Poor people derive overwhelmingly more value from dollar $10,001 than rich folks do from dollar $1,000,001. (This is not controversial.) Thus, rich folks can--and should because they derive more value from the structures of the society that enables them to be successful and not hit over the head for their paycheck--pay progressively more to sustain that society. (This is also not controversial in reality, even amongst relatively right-wing economists.)
(Note: I do understand about utility, and how/why progressive tax systems help society. My only bone of contention here is that you're trying to redefine a specific term to have a different meaning.)
And then everyone starts arguing about how progressive the system should be to do that properly. :-)