The GWWC pledge is akin to a flat tax, as opposed to a progressive tax—which gives you a higher tax rate when you earn more.
I agree that there are some arguments in favour of “progressive donations”.
One consideration is that extremely high “donation rates”—e.g. donating 100% of your income above a certain amount—may affect incentives to earn more adversely, depending on your motivations. But in a progressive donation rate system with a more moderate maximum donation rate that would probably not be as much of a problem.
The GWWC pledge is akin to a flat tax, as opposed to a progressive tax—which gives you a higher tax rate when you earn more.
I agree that there are some arguments in favour of “progressive donations”.
One consideration is that extremely high “donation rates”—e.g. donating 100% of your income above a certain amount—may affect incentives to earn more adversely, depending on your motivations. But in a progressive donation rate system with a more moderate maximum donation rate that would probably not be as much of a problem.