tbh I think the practice of giving away flat-rate 2.5% of their wealth each year instead of 40-50% brackets would encourage more wealthy people to actually donate and not dodge taxes.
Many very wealthy people already donate to charity as a form of tax avoidance, by showing that they are benefitting others therefore they should be allowed to dodge tax.
The main problems with the argument that if wealthy people didn't get taxed then they would donate to charity more are 1) it's not proven to be true 2) where the money goes gets decided by the donor.
For some people letting the donor decide where their money goes sounds like a good idea, as it's there money. However donors do not take a holistic view of the needs of a society and are very influenced by what visible to them, their opinions & prejudices, etc... For example rich people donate billions to Harvard University, which already has an endowment of over $40 billion, which benefits almost nobody. That's arguably not a great use of charity donations where there are other more pressing needs, also in education, which would be much more efficient uses of that money.
The wealthy also often think that they are best placed to solve problems that they have zero experience with, based on being successful in a completely different field. Typically this leads to failure or inefficient and suboptimal results.
Governments are not perfect, nowhere close, but in terms of taking a holistic view of the needs of society and applying funds where needed, they are generally much better than assigning that function to a financial elite, especially if that government is a social democracy.
