[repolfx]

Who underwrites the investment risks taken by Bill Gates exactly?

Wealth mobility in the USA is pretty high. It's entirely possible for billionaires to stop being billionaires, or for people to temporarily become rich and then lose it again. Lots of stories like that out there. Elon Musk has made fortunes and lost them several times, I think.

Taxation is not an illegal or immoral appropriation of property

Obviously it's not illegal by definition.

Immoral? Yeah, I think a 100% tax rate i.e. communism would be deeply immoral. And taxes today are very high, and frequently lead to huge misallocation of resources. I think you could easily argue for lower taxes from a moral position.