I'm talking about the US. You're looking at the simple version: just income. But the tax code is more than income--there are many benefits that go away at a specific AGI--if you use that benefit you can have an effective tax rate of over 100% in the realm just above the fence.

And your system doesn't work. Working is almost never truly free, you have to spend some money to make money. And you don't have that time available to do other things that stretch the money you have.