There are other ways to fix that: welfare, subsidies, philanthropy. We have that already.

We could still make everybody pay, say, a 25% of their income, no matter what, and only afterwards support financially the few at the very bottom who can’t make a living with what’s left to them.

It may seem the same, but it’s not.

First, we avoid the temptation of extending your argument from “a family which makes $50,000 a year” upward, multiple times. Those families which make $60,000 will still look with envy at those who make the double. And so on. Most people appear to “be rich” and to have “more than enough” to those who are immediately below them, no matter what.

Second, we understand that (at least in wealthy countries like the US and Spain), the default is that people make enough for a living, therefore everybody who earns any money should pay taxes, by principle. Taxes are deducted for everyone. Then, individual cases are considered. That would make claiming welfare the exception, and not the rule.

I suspect it’s simpler and more efficient to fix tax rates for everybody and use those taxes to help those in need, than trying to engineer a complex curve of tax brackets that would always feel unfair to most and complicate the tax code enormously (and then, having to help those in need too, anyway!).

With option A, society needs to fine-tune only two parameters: the tax rate, and the threshold for a “decent living”. Option B is a nightmare of cutoffs, percentages and tax exemptions.