I think it's a bit disingenuous to frame this problem as "we want to tax billionaires because they should pay more tax". While a small minority of people do act

I think it's a bit disingenuous to frame this problem as "we want to tax billionaires because they should pay more tax". While a small minority of people do actually feel that way, realistically the context is just about every government in the world is running a deficit nearly all the time and just about no one wants to lose programs they care about so we need some method of addressing that shortfall. Taxing the people who can most afford it, especially in ways that generate significant government revenue seems like the best solution to many.