I generally agree with you here, but as an aside there is one nuance you have to consider. And that's taxation vs disposable income. Imagine somebody earns $50k and spends $30k on their living expenses and pays a 30% tax rate. They have $20k left after their basic living expenses, but $15k of that is eaten up by taxes. Looking at their disposable income, they're paying a ridiculous tax rate of 75%.

I think it's more reasonable to compare taxation on disposable income. In my opinion a fair tax would only tax disposable income anyhow. Of course that creates an incentive to have $0 disposable income but it's no different than the problem of corporations aiming to report $0 profit.

Progressive tax schemes aim to achieve this, but in a completely broken and inconsistent fashion. For instance somebody earning $100k in San Francisco is going to be spending a rather different percent of their income on basic living expenses than somebody living in Bodunk earning the same, and so applying the same scheme to both does not make sense. It'd be much easier to just make everything that qualifies as a 'basic living expense' fully deductible, and then you pay e.g. 15% on the rest.