It's not primarily about income. It's about issuing new currency. Let's say the US government doubles the number of outstanding dollars. All other things being equal, once things settle out your dollar is going to have about half the purchasing power it had before the extra money was issued. It's a wealth tax.

But let's say you saw this coming and put your money into hard assets or stable foreign currencies. When you sell those assets or currencies, you have a huge paper gain which the USG is going to expect you to pay income taxes on even though you haven't made anything at all in constant dollars. Again, a wealth tax.