We can actually be certain that humans work the other way since we ran huge experiments in labs called the Soviet Union and China. In those experiments we found out that people worked way less/not at all when there was no economic incentive to do so.

I wonder why people endlessly argue how much they should tax the rich and the poor, there is only one answer: 100% of everything, i.e wealth, income, gifts etc. It's a nice round number and everybody is taxed fairly.

Agreed. After all, that is the equivalent rate for all work done in the commons, on free software for example. Zero dollars earned, but somehow the incentive is still there. Money is not the only thing that motivates human beings.

I believe this is why the income tax is so popular with economists. Other taxes create some type of negative feedback where raising the tax decreases transactions and shifts capital elsewhere. But with the income tax people have no choice but to keep working and may even have to work more. So the "economy" benefits because more labor/capital can be squeezed out of individuals without slowing anything down.