Sure it does, because if you have deductions, your effective tax rate isn't actually flat.

> Removing deductions has nothing to do with the tax curve. You could do that with the current curve and tweak it accordingly.

In theory, but (serious) advocates of the flat tax generally are proposing both.

My impression is that most advocates want the flat part which reduces taxes on high incomes and then are pretty hand wavy about deductions.

This might be the case in the US, but be aware that most advocates of flat taxes globally - including almost all economists who do so - advocate precisely for removing deductions.

In New Zealand, for example, all prominent advocates of flat taxes are also proponents of not following Australia or the UK's example of having GST/VAT exemptions for some categories of goods.

In fact, removing itemized deductions alone would do this, because the standard deduction is mathematically equivalent to a 0% bracket.

Alternately, you could even have a progressive, flat tax with a standard deduction of $150,000 and like a 40% rate. I’m surprised the Democrats haven’t proposed that just as a publicity stunt.

Deductions are not entirely equivalent to a 0% bracket in a progressive tax scheme, they come out of top bracket income.

So high earners get a larger tax reduction from deductions than low earners. There's not really a way to do that with a 0% bracket (and in fact we have both a 0% bracket and deductions).