The argument for billionaires seems to that (i) they innovated and developed the company and you can't discourage that and (ii) their assets are not like a traditional income and it is difficult to tax something that is just sitting and growing.
Regarding the first point, there are multiple factors that have led to extreme wealth such as practically abandoning monopoly policing, BOTs being just CEOs/founders' buddies, public resources (telecom bands, natural resources, etc.) being privatized in short-sighted sales, etc. Bezos won't be so rich if Amazon was broken up into at least 3 units (Amazon.com, AWS and services such as Kindle, Ring, Alexa, etc.) and there was actual penalization on fake reviews and products that don't live up to what is advertised, collective voice for their low-wage packers and drivers, etc. Same thing with Google, Apple, etc. They in their state are stifling innovation lot more than enabling.
Regarding BOTs, I remember in my last company where a ~1000 employee company board approved 1M shares for annual RSU distribution, and allotted 500k to the CEO, 250k to his direct reports, 150k to the various VPs and the remaining 100k for everyone else from director downwards. This is with the salary of CEO being >10x of a director and >50x of a lowest paid office employee. And that CEO was quite incompetent.
About taxing the extremely wealthy, do what I (Muslim) have to do. Every year, I have to give 2.5% of my disposable wealth to the poor and needy. Anything outside of the things I use daily such as my house, car, clothes etc. is disposable wealth. If I have 100k in stocks, I have to sell 2.5k worth and give it away. I think 2.5% of disposable wealth (anything in a bank, in investment, in inventory, etc.) will be many times more than what is needed to provide basic necessities for not just US but the whole world.